Karl Julius Beloch (January 21, 1854 – February 1, 1929) was a German classical and economic historian.
In 1870 he moved to Italy for health reasons, where he subsequently studied in Palermo and Rome. In 1875 he received his doctorate from the University of Heidelberg. In 1879 he became a professor extraordinarius of ancient history at the University of Rome, where he remained for almost all of his professional career.
Beloch is known for his critical examinations of classical Greek and Roman history. He was skeptical of traditional sources, and frequently presented a new and subjective reconstruction of historical events. These viewpoints placed him out of favor with several influential German scholars, particularly famed historian Theodor Mommsen. In 1889 Beloch was denied professorship at Breslau, a position which had been vacated by Eduard Meyer, and instead given to Ulrich Wilcken.
Among his numerous publications was a four-volume opus of Greek history titled Griechische Geschichte, and a systematic study involving the demography of the Greco-Roman world called Die Bevölkerung der griechisch-römischen Welt.