From 542 to 562, Lazica was a scene of the protracted rivalry between the Eastern Roman and Sassanid empires, culminating in the Lazic War, where 1,000 Tzanni auxiliaries under Dagisthaeus participated. Emperor Heraclius's offensive in 628 AD brought victory over the Persians and ensured Roman predominance in Lazica until the invasion and conquest of the Caucasus by the Arabs in the second half of the seventh century. As the result of Muslim invasions, the ancient metropolis, Phasis, was lost and Trebizond became the new Metropolitan bishop of Lazica, since then the name Lazi appears the general Greek name for Tzanni. According to Geography of Anania Shirakatsi of the 7th century, Colchis ("Yeger" in Armenian sources, same as Lazica) was subdivided into four small districts, one of them being Tzanica, that is Chaldia, and mentions Athinae, Rhizus and Trebizond among its cities. From the second half of the eight century the Trebizond area is referred to in Greek sources (namely of Epiphanius of Constantinople) as Lazica. The 10th-century Arab geographer Abul Feda regards city of Trebizond as being largely a Lazian port.