There were, for a long but uncertain period, a significant number of Jews in Arabia. Historians claim that very large numbers of Jews – as many as 80,000 – arrived after the destruction of the First Temple, to join others already long-established in places such as the oasis of Khaybar as well as the trading colonies in Medina and Mecca (where they had their own cemetery). Another theory posits that these Jews were refugees from Byzantine persecutions. Arab historians mention some 20 Jewish communities, including two of Kohanim.