What made Byzantium rich?

Byzantium became rich mainly through trade with its neighbors. The best goods and products went abroad, this is how the country’s economic fund was accumulated. They took out jewelry, wine, fabrics, various dishes with gold painting. Also, the administrators of Byzantium sold the right to citizenship. It consisted in the fact that coming to Byzantium, any foreigner could acquire citizenship for a certain amount, after which he was considered a full resident. The Byzantines worked well with leather and furs, made fur coats for kings and nobles.