Byzantine–Arab Wars (780–1180)

Byzantine–Arab Wars (780–1180)
Part of the Byzantine-Arab Wars
Date 780–1180
Location Anatolia, Mesopotamia, Syria, Sicily, Southern Italy and Palestine.
Result status quo uti possidetis.
Territorial
changes
See Conclusion.
Belligerents
Byzantine Empire
Holy Roman Empire[1]
Italian city-states
Crusader states
Fatimid Caliphate
Abbasid Caliphate
Uqaylids
Hamdanids
Emirate of Sicily
Emirate of Crete
Commanders and leaders
Byzantine Emperors
Strategoi of the Themata
Drungaries of the Fleets
Fatimid Caliphate rulers
Abbasid Caliphate
Strength
Total Strength 80,000 in 773
Total Strength 250,000 in 1025
Total Strength 50,000 + militia in 1140
Abbasid Strength 100,000 in 781[2]
Abbasid Strength 135,000 in 806[2][3]

Between 780–1180, the Byzantine Empire and the Abbasid & Fatimid caliphates in the regions of Iraq, Palestine, Syria, Anatolia and Southern Italy fought a series of wars for supremacy in the Eastern Mediterranean. After a period of indecisive and slow border warfare, a string of almost unbroken Byzantine victories in the late 10th and early 11th centuries allowed three Byzantine Emperors, namely Nikephoros II Phocas, John I Tzimiskes and finally Basil II to recapture territory lost to the Muslim conquests in the 7th century Byzantine-Arab Wars under the failing Heraclian Dynasty.[4]

Consequently large parts of Syria,[4] including its capital city of Damascus, were taken by the Byzantines, even if only for a few years, with a new theme of Syria integrated into the expanding empire. In addition to the natural gains of land, and wealth and manpower received from these victories, the Byzantines also inflicted a psychological defeat on their opponents by recapturing territory deemed holy and important to Christendom, in particular the city of Antioch—allowing Byzantium to hold two of Christendoms' five most important Patriarchs, those making up the Pentarchy. [5]

Nonetheless, the Arabs remained a fierce opponent to the Byzantines and a temporary Fatimid recovery after c. 970 had the potential to reverse many of the earlier victories.[6] And while Byzantium took large parts of Palestine, Jerusalem was left untouched and the ideological victory from the campaign was not as great as it could have been had Byzantium recaptured this fourth Patriarchal seat of Christendom. Byzantine attempts to stem the slow but successful Arab conquest of Sicily ended in a dismal failure.[7] Syria would cease to exist as a Byzantine province when the Turks took the city of Antioch in c. 1084. The Crusaders took the city back for Christendom in 1097 but a Byzantine protectorate was established over the Crusader Kingdoms in Jerusalem and Antioch under Manuel I Komnenos.[8] The death of Manuel Komnenos in 1180 terminated military campaigns far from Constantinople and after the Fourth Crusade both the Byzantines and the Arabs were engaged in other conflicts until they were conquered by the Ottoman Turks in the 15th and 16th centuries, respectively.

Contents

Background, 630–780

From c. 630, the Byzantine Empire came under attack from the Arabs in present day Saudi Arabia. Having recently converted to Islam and unified by the Islamic Prophet's call for a Jihad (struggle) against the Byzantine and Persian Empires, they rapidly advanced and took advantage of the chaos of the Byzantine Empire, which had not fully consolidated its "re-acquisitions" from the Persian invasions in c. 620. By 641, the Empire had lost Egypt, Palestine, Syria and Mesopotamia.[9] Despite having lost two-thirds of its land and resources (most of all the grain supply of Egypt) the Empire nonetheless retained 80,000 troops, thanks to the efficiency of the Thema system and a reformed Byzantine economy aimed at supplying the army with weapons and food.[10] With these reforms, the Byzantines were able to inflict a number of defeats against the Arabs; twice at Constantinople in 674 and 717 and at Akroinon in 740.[11] Constantine V, the son of Leo III (who had led Byzantium to victory in 717 and 740) continued the successes of his father by launching a successful offensive that captured Theodosioupolis and Melitene. Nonetheless, these conquests were temporary; the Iconoclasm controversy, the ineffective rule of Irene and her successors coupled with the resurrection of the Western Roman Empire under the Frankish Carolingian Empire and Bulgarian invasions meant that the Byzantines were on the defensive again.

Period of 820–842

Michael II Vs Caliph Al-Ma'mun

Between 780 and 824, the Arabs and the Byzantines were settled down into border skirmishing, with Arab raids into Anatolia replied in kind by Byzantine raids that "stole" Christian subjects of the Abbasid Caliphate and forcibly settled them into the Anatolian farmlands to increase the population (and hence provide more farmers and more soldiers). The situation changed however with the rise to power of Michael II in 820. Forced to deal with the rebel Thomas the Slav, Michael had few troops to spare against a small Arab invasion of 40 ships and 10,000 men against Crete, which fell in 824.[12] A Byzantine counter in 826 failed miserably. Worse still was the invasion of Sicily in 827 by Arabs of Tunis.[12] Even so, Byzantine resistance in Sicily was fierce and not without success whilst the Arabs became quickly plagued by the cancer of the Caliphate— internal squabbles. That year, the Arabs were expelled from Sicily but they were to return.

Theophilos Vs Caliphs Al-Ma'mun and Al-Mu'tasim

In 829, Michael II died and was succeeded by his son Theophilos. Theophilos received a mixed diet of success and defeat against his Arab opponents. In 830 AD the Arabs returned to Sicily and after a year-long siege took Palermo from their Christian opponents and for the next 200 years they were to remain there to complete their conquest, which was never short of Christian counters.[13] The Abbasids meanwhile launched an invasion of Anatolia in 830 AD. Al-Ma'mun triumphed and a number of Byzantine forts were lost. Theophilos did not relent and in 831 captured Tarsus from the Muslims.[14] Defeat followed victory, with two Byzantine defeats in Cappadocia followed by the destruction of Melitene, Samosata and Zapetra by vengeful Byzantine troops in 837. Al-Mu'tasim however won the last laugh in 838 with victories at Dazimon, Ancyra and finally at Amorium[14]—the latter sacking is presumed to have caused great grief for Theophilos and was one of the factors of his death in 842.

Campaigns of Michael III, 842–867

Michael III was only two years of age when his father died. His mother, the Empress Theodora took over as regent. After the regency had finally removed Iconoclasm, war with the Saracens resumed. Although an expedition to recover Crete failed in 853, the Byzantine scored three major success in 853 and 855. A Byzantine fleet sailed unopposed in Damietta and set fire to all the ships in the harbour, returning with many prisoners.[15] Better still for Constantinople was the desperate and futile defense by the Emir of Melitene, whose realm was lost by the Arabs forever.[16] Insult was added to injury for the Arabs when the Arab governor of Armenia began losing control of his domain. After the 9th century, the Arabs would never be in a dominant position in the East.

In the West however, things went the Saracen way; Messina and Enna fell in 842 and 859 whilst Islamic success in Sicily encourage the warriors of the Jihad to take Bari in 847, establishing the Emirate of Bari which would last to 871. In invading southern Italy, the Arabs attracted the attention of the Frankish powers north.

Michael III decided to remedy the situation by first taking back Crete from the Arabs. The island would provide an excellent base for operations in southern Italy and Sicily or at the least a supply base to allow the still resisting Byzantine troops to hold out. In 865 Bardas, maternal uncle to Michael III and one of the most prominent members of his regency, was set to launch an invasion when a potential plot against his wife by Basil I and Michael III (the former being the future emperor and favorite of the latter) was discovered. Thus Islamic Crete was spared from an invasion by Byzantium's greatest general at the time.[17]

Campaigns of Basil I and Leo VI, 867–912

Basil I

Like his murdered predecessor, the reign of Basil I saw a mixture of defeat and victory against the Arabs. Byzantine success in the Euphrates valley in the East was complemented with successes in the west where the Saracens were driven out of the Dalmatian coast in 873 and Bari fell to the Byzantines in 876.[18] However, Syracuse fell in 878 to the Sicilian Emirate and without further help Byzantine Sicily seemed lost.[18] Further success would wait Basil I when Taranto and much of Calabria fell in 880 to Imperial troops. Calabria had been Rome's pre-Aegyptus bread basket, so this was more than just a propaganda victory.

Leo VI

Basil I died in 886, convinced that this son Leo VI the Wise was actually the bastard of Michael III from his mistress Eudokia Ingerina. If so, then the Macedonian renaissance of the Byzantine Empire is nothing more than a continuation of the successful policies of the Amorian dynasty. Leo VI's reign saw even smaller and less impressive results against the Arabs. The savage sack of Thessalonika in 904 by the Saracens of Crete was avenged when a Byzantine army and fleet smashed its way towards Tarsus and left the port, equally important to the Arabs as Thessalonika was to Byzantium, in ashes.[19] The only other notable events included the loss of Taormina in 902 and a six-month siege of Crete. The expedition departed when news of the Emperor's death reached Himerios, commander of the expedition, and then it was almost completely destroyed (save Himerios who escaped) not far from Constantinople.[20]

Romanos I and Constantine VII, 920–959

Up till now the Byzantine Empire was concerned solely with survival and with holding on to what they already had. Numerous expeditions to Crete and Sicily were sadly reminiscent of the failures of Heraclius, even though the Arab conquest of Sicily did not go according to plan. After Leo's death in 912 the Empire became embroiled in problems with the regency of the seven-year old Constantine VII and with invasions of Thrace by Simeon I of Bulgaria.[21]

The situation changed however when the admiral Romanos Lekapenos assumed power as a co-emperor with Constantine VII and three of his rather useless sons, thus ending the internal problems with the government. The Bulgar problem meanwhile more or less solved itself with the death of Simeon in 927, so John Kourkouas of the Byzantines was able to from 923 to c 950 AD campaign aggressively against the Saracens.[22] Armenia was consolidated within the Empire whilst Melitene which had been a ruined emirate since the 9th century was annexed at last. In 941 John Kourkouas was forced to turn his army north to fight off the invasion of Igor I of Kiev but was able to return to lay siege to Edessa—no Byzantine army had reached so far since the days of Heraclius. In the end the city was able to maintain its freedom when Al-Muttaqi agreed to give up a precious Christian relic: the "Image of Edessa".[23]

Constantine VII assumed full power in 945. Whilst his predecessor, Romanos I had managed to use diplomacy to keep peace in the West against the Bulgars, the East required force of arms to create any such peace. Constantine VII turned to his most powerful ally, the Phocas family. Bardas Phokas the Elder had originally supported the claims of Constantine VII against those of Romanos I and coupled with his position as strategos of the Armeniakon Theme made him the ideal candidate for warring with against the Caliphate.[24] Even so, Bardas was wounded in 953 without much success but his son Nikephoros Phokas was able to inflict a serious defeat on the Caliphate: Adata fell in 957 whilst Nikephoros' young nephew, John Tzimiskes, captured Samosata in the Euphrates valley in 958.[24]

Romanos II, 959–963

Romanos II launched Byzantium's greatest ever expedition since the days of Heraclius. A mammoth force of 50,000 men, 1,000 heavy transports, over 300 supply ships and some 2,000 Greek Fire Ships under the brilliant Nikephoros Phokas set sail for Candia, the Islamic capital of Crete.[25] After an eight-month siege and a bitter winter,[25] Nikephoros sacked the city. News of the reconquest was met with great delight in Constantinople with a night-long service of thanksgiving given by the Byzantines to God in the Hagia Sophia.[26]

Nikephoros saw none of this gratitude, being denied a triumph due to Romanus II's fear of feeding his ambitions. [26] Instead, Nikephoros had to march rapidly to the East where Saif al-Daula of the Hamdanid dynasty, the Emir of Aleppo, had taken 30,000 men into Imperial territory,[26] attempting to take advantage of the army's absence in Crete. The Emir was one of the most powerful independent rulers in the Islamic world—his domains included Damascus, Aleppo, Emesa and Antioch.[26] After a triumphant campaign, Saif was bogged down with overwhelming numbers of prisoners and loot. Nikephoros' brother Leo Phokas was unable to engage the Emir in an open battle with his small army. Instead, Saif found himself fleeing from battle with 300 cavalry and his army torn to pieces by a brilliantly planned ambush in the mountain passes of Asia Minor. With great satisfaction, Christian captives were substituted with recently acquired Muslims.[27]

When Nikephoros arrived and linked up with his brother, their army did no few wonders—a few weeks into 962 and some 55 walled towns in Cilicia returned to Imperial control.[27] Not many months had passed when the Phokas brothers were beneath the walls of Aleppo. The city was utterly ruined when the Byzantines stormed it on December 23, save for the citadel which was zealously held by a few soldiers of the Emir. The beautiful palace of Aleppo was outside the walls—it is easy to imagine how many stones were left untouched in the carnage. With Christmas at hand and the Byzantine troops having thoroughly reduced the place, Nikephoros ordered a withdrawal; the Emir of Aleppo had been too badly beaten to pose a threat anymore.[27] The troops at the citadel still holding out were ignored with contempt. Nikephoros' army had not left Cappadocia when news of Romanos II's death reached him.

Byzantine resurgence, 963–1025

Nikephoros II Phocas, 963–969

Romanos II left behind Theophano, a beautiful empress widow and four children, the eldest son being less than seven years. Like many regencies, that of Basil II proved chaotic and not without scheming of ambitious generals such as Nikephoros or internal fighting, between Macedonian levies, Anatolians and even the pious crowd of the Hagia Sophia.[28] When Nikephoros emerged triumphant in 963 AD, he once more began campaigning against his Saracen opponents in the East.

In 965 Tarsus fell, followed by Cyprus that same year.[5] In 967 the defeated Saif of Mosul died of a stroke,[5] thus depriving Nikephoros of the only serious challenge there (Said had not fully recovered from the sack of Aleppo). Aleppo became an imperial vassal shortly after. In 969, the city of Antioch was retaken by the Byzantines.[5] Antioch was the first major city in Syria to be lost by the Arabs. Byzantine success was not total, and in 964 another failed attempt was made to take Sicily. Having taken Crete and Cyprus himself, one could forgive Nikephoros for believing that he was on a roll for capturing Arab-held islands. In 969, Nikephoros was murdered in his palace by John Tzimiskes who took the throne for himself.[29]

John I Tzimiskes, 969–976

In 971 the new Fatimid Caliphate entered the scene. With similar newly found zeal they took Egypt, Palestine and much of Syria from the powerless Abbasids, who were beginning to have their own Turkic problems.[6] Having defeated their Islamic opponents, the Fatimids saw no reason to stop at Antioch and Aleppo, cities in the hands of the Christian Byzantines, and their conquest being more important. A failed attack on Antioch in 971 was followed up by a Byzantine defeat outside of Amida.[6] However, John I Tzimiskes would prove to be a greater foe than Nikephoros. With 10,000 Armenian troops and other levies he pushed south, relieving the Imperial possessions there and threatening Baghdad with an invasion. His reluctance to invade the Abbasid Capital, though poorly defended and demoralized, remains a mystery.[6]

After dealing with more Church matters, John returned in the Spring of 975. As the Ummayad conquests were halted after roughly a hundred years, John cut the initial success of the Fatimid Caliphate even sooner: Syria, Lebanon and much of Palestine fell to the imperial armies of Byzantium.[30] It appears that John's sickness that year and the year after halted his progress and saved Jerusalem from a Christian victory.

Basil II the Bulgar Slayer, 976–1025

The early reign of Basil II was distracted with civil wars across the Empire. After having finally dealt with the invasions of Samuel of Bulgaria and pardoned/destroyed the revolts of Bardas Phokas and Bardas Skleros, Basil turned his attention in 995 to Syria, where the Emir of Aleppo was in danger.[31] As an imperial vassal the Emir pleaded to the Byzantines for military assistance, since the city was under the siege of Abu Mansoor Nizar al-Aziz Billah. Basil II rushed back to Constantinople with 40,000 men; he gave his army some 80,000 mules, one for each soldier and another for their equipment.[31] The first 17,000 men arrived with great speed before Aleppo and the hopelessly outnumbered Fatimid army withdrew. Basil II pursued it south, sacking Emesa and reaching as far as Tripoli.[31] Basil returned to the Bulgar front with no further campaigning against the Saracen foe.

Final battles

The Byzantine Empire would not produce an Emperor worthy of Constantinople until 1081, when Alexius I Comnenus seized power and re-initiated the Komnenian dynasty. Until then however, minor Byzantine successes against the Arabs masked the decline of the Empire. The Arab world as a potent military force had been in decline since the 9th century; losses in Mesopotamia, Syria and the slow conquest of Sicily proved this. Now Byzantium would experience that same decline.[32]

Constantine VIII's short and uneventful reign was followed up by the incompetent Romanos III. When Romanos marched his army to Aleppo he was ambushed by the Arabs.[33] The power of Byzantium is demonstrated by the fact that despite Romanos' failure, his general George Maniaces was able to recover the situation and defend Edessa against Arab attack in 1032. This however reveals another nature to Byzantium - the decentralized nature of the army, which could operate effectively even with an incompetent general - something that future ill-conceiving Byzantine generals would use to plunge the Empire into chaos.

Romanos III's successor (and possibly his murderer) Michael IV the Paphlagonian saw the expedition against Sicily under George Maniaces. Initial Byzantine success saw Messina falling in 1038 followed by Syracuse in 1040 but the expedition was riddled with internal strife and was diverted to a more disastrous course against the Normans in Italy, who were beginning to add southern Italy to Byzantium's long list of lost provinces.[7]

Following the loss of Sicily and most of southern Italy, the Byzantine Empire collapsed into a state of petty inter-governmental strife. Isaac I Komnenos took power in 1059[34] but his brief two year rule cut his reforms short. The Fatimid and Abbasid Caliphate were already busy fighting the Seljuq dynasty; the Byzantines woke up to this threat under Romanos IV, co-emperor of Byzantium. At the 1071 Battle of Manzikert, the Byzantines were defeated by Alp Arslan , Head of the Great Seljuq Empire.[35][36] This, coupled with a civil war, brought most of the Asia Minor under the rule of the Seljuq Turks by 1091.[4] Despite a recovery under Alexios I Comnenus, the Byzantines would not fight the Arabs again until the end of the reign of John II Comnenus.

Komnenian-Arab Wars

John II Komnenos pursued a pro-Crusader policy, actively defending the Crusader states against the forces of Zengi. His army marched and laid siege to Shaizar, but the Principality of Antioch betrayed the Byzantines with inactiveness.[37] John II therefore had little choice but accept the Emir of Mosul's promise of vassalage and annual tribute to Byzantium.[37] The other choice would have been risking a battle whilst leaving his siege equipment in the hands of the untrustworthy Crusaders. John could have beaten Zengi, but Zengi was not the only potential foe for Byzantium.

John II died in 1143. The foolishness of the Principality of Antioch meant that Edessa fell and now the great Patriarchate was on the front line.[38] A failed siege on Damascus in the Second Crusade forced the Kingdom to turn south against Egypt.[39] The new Byzantine Emperor, Manuel I Komnenos enjoyed the idea of conquering Egypt - whose vast resources in grain and in native Christian manpower (from the Copts) would be no small reward, even if shared with the Crusaders. Alas, Manuel Komnenos worked too quickly for the Crusaders. After three months the Siege of Damietta in 1169 failed,[40] although the Crusaders received a mixed diet of defeat (with several invasions failing) and some victories. The Crusaders were able to negotiate the Fatimids to surrender the capital to a small Crusader garrison and pay annual tribute,[41] but a Crusader breach of the treaty coupled with the rising power of the Muslims saw Saladin master of Syria and Egypt.

In 1171, Amalric I of Jerusalem came to Constantinople in person, after Egypt had fallen to Saladin.[42] In 1177, a fleet of 150 ships was sent by Manuel I to invade Egypt, but returned home after appearing off Acre due to the refusal of Philip, Count of Flanders and many important nobles of the Kingdom of Jerusalem to help.[43]

In that year Manuel Komnenos suffered a defeat in the Battle of Myriokephalon against Kilij Arslan II of the Seljuk Sultanate of Rûm.[44] Even so, the Byzantine Emperor continued to have an interest in Syria, planning to march his army south in a pilgrimage and show of strength against Saladin's might. Nonetheless, like much of Manuel's goals, this proved unrealistic and he had to spend the last of his years until his death in 1180 working hard to restore the Eastern front against Iconium, which had deteriorated somewhat in the time wasted in fruitless Arab campaigns.

Conclusion

Like all of Byzantium's wars, all gains made were temporary reconquests. By the mid-9th century the Arabs had been for the most part driven out of the gates of Cilicia. However, they seized Cyprus and in the 9th century took both Sicily and after Crete with fewer troops then sent against Constantinople in 717. The Byzantines' counter-attack came in the late 9th century under the Macedonian Emperors, defeating the Emir of Melitene and weakening Arab rule over Armenia. In the mid 10th century, the Island of Sicily was totally overrun, but the south of Italy and Illyria survived. Under Nikephoros Phocas, Cilicia and small parts of northern Syria, including Antioch was reconquered. Cyprus and Crete also fell to Imperial forces. John Tzimiskes made one large offensive into Mosul and Palestine, withdrawing to face the Bulgar threat. When Basil II came to power, the Arabs had completed their conquest of Sicily, but lost most of Syria.

With the arrival of the Seljuk Turks, all territories except western Anatolia, the coast of Syria, Greece and Illyria were lost.

It would take another 100 years and several wasted opportunities (for both sides) before the Crusader states were wiped out. By then, the Byzantines Empire slipped into decline (1180–1203), was sacked and splintered (1204–1261) and never recovered its position to fight on a front so far from Constantinople. Within 200 years of the Palaiologan restoration, the Byzantine Empire was eliminated with the fall of Trebizond in 1461 whilst Egypt fell 60 years later in 1520 under the Ottoman Sultan Selim I.

See also

Notes

  1. ^ Occasional alliances against Saracen piracy were concluded
  2. ^ a b Kennedy, Hugh (2001). The Armies of the Caliphs: Military and Society in the Early Islamic State. pp. p. 99. 
  3. ^ Even if Byzantium had survived the worst the Arabs could do, its troubles were far from over. The caliphate was still much stronger than the empire. Warren Treadgold, The Oxford Dictionary of Byzantium, pg 138.
  4. ^ a b c Magdalino, Paul (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 180. 
  5. ^ a b c d Norwich 1997, p. 192
  6. ^ a b c d Norwich 1997, p. 202
  7. ^ a b Norwich 1997, p. 221
  8. ^ Magdalino, Paul (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 189. 
  9. ^ Treadgold, Warren (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 131. 
  10. ^ Treadgold, Warren (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 144. 
  11. ^ Treadgold, Warren (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 139. 
  12. ^ a b Magdalino, Paul (2002). The Oxford History of Byzantium. New York: Oxford UP. pp. p. 171. 
  13. ^ Norwich 1997, p. 134
  14. ^ a b Norwich 1997, p. 137
  15. ^ Norwich 1997, p. 140
  16. ^ Norwich 1997, p. 141
  17. ^ Norwich 1997, p. 149
  18. ^ a b Norwich 1997, p. 155
  19. ^ Norwich 1997, p. 161
  20. ^ Norwich 1997, p. 164
  21. ^ Norwich 1997, p. 168–174
  22. ^ Norwich 1997, p. 174
  23. ^ Norwich 1997, p. 177
  24. ^ a b Norwich 1997, p. 181
  25. ^ a b Norwich 1997, p. 184
  26. ^ a b c d Norwich 1997, p. 185
  27. ^ a b c Norwich 1997, p. 186
  28. ^ Norwich 1997, pp. 187–190
  29. ^ Norwich 1997, p. 197
  30. ^ Norwich 1997, p. 203
  31. ^ a b c Norwich 1997, p. 212
  32. ^ Norwich 1997, p. 217. The title page reads, "The Decline Begins, 1025 - 1055"
  33. ^ Norwich 1997, p. 218
  34. ^ Norwich 1997, p. 234
  35. ^ Norwich 1997, p. 240
  36. ^ Haldon 2002, pp. 45–46
  37. ^ a b Norwich 1997, p. 271
  38. ^ Norwich 1997, p. 272: "Not only had they made no further progress against the Saracens; they had failed even to preserve John's earlier conquests"
  39. ^ Norwich 1997, p. 279
  40. ^ Madden 2004, p. 69
  41. ^ Madden 2004, p. 68
  42. ^ Magdalino 1993, p. 75
    * H.E. Mayer, The Latin East, 657
  43. ^ J. Harris, Byzantium and The Crusades, 109
  44. ^ Madden 2004, p. 71

References and further reading