Few contemporary sources mention Crete during the period from the 4th century to the Muslim conquest in the 820s. During this time, the island was very much a quiet provincial backwater in the periphery of the Greco-Roman world. Its bishops are even absent from the First Council of Nicaea in 325, in contrast to neighbouring islands like Rhodes or Kos. With the exception of an attack by the Vandals in 457 and the great earthquakes of 9 July 365, 415 448 and 531, which destroyed many towns, the island remained peaceful and prosperous, as testified by the numerous, large and well-built monuments from the period surviving on the island. In the 6th-century "Synecdemus", Crete is marked as being governed by a "consularis", with capital at Gortyn, and as many as 22 cities. The population in this period is estimated as high as 250,000, and was almost exclusively Christian, except for some Jews living in the main urban centres.