What is Defensor Civitatis?

Legal Definition
Defender or protector of a city or municipality. An officer under the Roman empire, whose duty it was to protect the people against the injustice of the magistrates, the insolence of the subaltern officers, and the rapacity.of the money-lenders. Schm. Civil Law, Introd. 16; Cod. 1, 55, 4. He had the powers of a judge, with jurisdiction of pecuniary causes to a limited amount, and the lighter species of offenses. Cod. 1, 55, 1; Nov. 15, e. 3, ยง 2; Id. c. 6, 1: He had also the care of the public records, and powers similar to those of a notary in regard to the execution of wills and conveyances.
-- Black's Law Dictionary