The first mention of Jews in the areas of modern-day Saudi Arabia dates back, by some accounts, to the time of the First Temple. Immigration to the Arabian Peninsula began in earnest in the 2nd century CE, and by the 6th and 7th centuries there was a considerable Jewish population in Hejaz, mostly in and around Medina. This was in part due to the embrace of Judaism by such leaders as Dhu Nuwas; who was very aggressive about converting his subjects to Judaism. Nuwas persecuted Christians in his kingdom as a reaction to the Christian persecution of Jews by the local Christians and Abu Karib Asad. In 523, the Himyarite king Dhu Nuwas (Dunaan), who had converted to Judaism, massacred the Christians there.