A prime factor in the development of Salonika into an economic center was its complex rabbinical authority. This stemmed from, according to K.E. Fleming, the rabbis' openness and tolerance of different groups of people. This is especially true of conversos, or Jews whose families converted to Christianity whilst living in Spain or Portugal in order to avoid persecution or potential expulsion. A common practice among conversos who wished to live in Salonika was the practice of Teshuvah. This was the concept of Jews returning to Judaism after previously converting, or after an ancestor converted. According to Fleming, the number of conversos returning to the faith whilst also immigrating to Salonika, made for a dynamic rabbinic establishment. In many cases, the process of reconverting back to Judaism was automatic and it required no extended arbitration by the rabbis. The kehalim—or congregations of Salonika—wanted to make sure that the process of Teshuvah was as smooth as possible for the participants. The process had gone on for centuries before the modern era. Multiple responsums document the Teshuvah proceedings. In one instance, a converso man claimed that he was Jewish in his father's side and was accepted back into the Jewish faith. This willingness to accept those back into the faith, made Salonika into an economic powerhouse, much to the ire of Greece. By the late 1800s, Salonika had grown to be much larger and more prosperous than Athens, and a target of Greek conquest.
