One of Wessely's ancestors, Joseph Reis, fled from Podolia in 1648 on account of the Chmielnicki persecutions, during which his whole family had perished. After a brief sojourn in Cracow, Reis settled in Amsterdam, where he acquired great wealth, and where he, in 1671, was one of the signers of a petition to the Dutch government requesting permission to erect a synagogue. Together with his younger son, Moses (Moses Reis(-)Wessely), Reis later settled in Wesel on the Rhine, whence the family name "Wessely" originated. In the synagogue at Wesel are still (as of 1906) preserved some ritual paraphernalia presented to it by Moses Reis Wessely, who, upon the advice of the Prince of Holstein, whose purveyor he was, removed to Glückstadt, then the capital of Sleswick. He established there a factory of arms. King Frederick VI of Denmark later sent Moses to Hamburg as his agent, and while there he transacted important business for Peter the Great also.