Cassandrea, Cassandreia, or Cassandria (Ancient Greek: Κασσάνδρεια, Kassandreia) was once one of the most important cities in Ancient Macedonia founded by and named after Cassander in 316 BC located on the site of the earlier Ancient Greek city of Potidaea. The fact that Cassander named it after himself suggests that he may have intended it to be his capital, and if the canal which cuts the peninsula at this point was dug or at least planned in his time, he may have intended to develop his naval forces using it as a base with two harbours on the east and west sides. The territory also at one time comprised the areas of Olynthus and Mekyberna to the northeast, Bottiaea to the northwest and the small peninsula of Pallene (now Kassandra) to the east. At the end of the Roman Republic, a Roman colony was settled around 43 BC by the order of Brutus, by the proconsul Q. Hortensius Hortatus. The official colonial name was Colonia Iulia Augusta Cassandrensis. The colony enjoyed ius Italicum. It is mentioned in Pliny the Elder's encyclopaedia (IV, 36) and in inscriptions.
During the Byzantine period it was briefly important in the 1423–30 period, when the Venetians captured it from the Turks and used it as a naval base. They also captured the castle of Platamon on the western shore of the Thermaic Gulf, and so had complete control of the approaches by sea to Thessalonica, which they had taken over after it had been offered to them by the ruling Despot. Like Thessalonica, it fell to the Ottomans in 1430.
The modern settlement of Kassandra lies to the south of the ancient site. The ancient site of Cassandreia (renamed Nea Potidaia) is not excavated. The peninsula of Pallene, now generally known as Kassandra, stretches to the south. This was the westernmost of the three peninsulas of Chalkidike, the middle one being the Sithone/Torone peninsula and the easternmost Mount Athos. Its southernmost point is near Paliouri which is also the prefecture's southernmost point; the promontories include the Kassandreia to the west and the Kanistro to the east. Except for Kanastraio, none of these capes marks the extremities of the peninsula except for the eastern part.
The canal on the northern side of Nea Potidaia to the north divides the peninsula from the rest of Chalkidiki.
The peninsula of Kassandra features picturesque villages, beautiful green nature filled with grasslands and forests, beaches and tourist attractions.
Kassandra was one of the places that rebelled against the Ottomans in 1821. Because it managed to stop the Turkish army from fighting the south Greece rebels it was burnt from edge to edge. The refugees moved with fishing boats to the islands of Skiathos, Skopelos, Alonissos and Evoia. Nobody lived in the peninsula for more than 30 years. Then the population started to gather again. In 1912 it became a part of Greece.
The peninsula was lined with paved road in the mid-20th century. Tourism also arrived beginning after the war period of World War II and the Greek Civil War. More paved roads were added in the 1970s and the 1980s and tourism popped out. Agriculture shifted to tourism and other businesses as its primary industry in the 1980s.
On August 22, 2006, the peninsula was struck by a major forest fire (see also Forest fires in Greece, 2006) that affected the central and the southern parts of the peninsula, the day of the heatwave when temperatures soared nearly 40 °C. Several houses were destroyed including villas, hotels and one campground disappeared as the natural beauty was to be erased. It burnt about 1,000 to 20 square kilometres of forests including some farmlands. Aerial pictures were reported near Sani Beach inland to a point where pastures and mountain roads are located and saw smoke throughout the peninsula. It can be seen across the gulf. The cause of this tremendous fire was dry lightning occurred throughout the evening. Power were cut to all affected villages. The forest fire lasted nearly five days and devastated the economy and the peninsula. All roads in the southern part were closed. Villages that were affected were Chanioti, Nea Skioni, Polychrono, Pefkochori, Kriopigi, Kassandrino and near the coastline.
Cassandreia is twinned with the following cities: