"the full faith and credit"... the legions fought to keep the market safe (where their families too came to buy and sell) and the market fought in his own way to provide anything needed to defend the market (and everything else). it's a symbiotic relation. the rest is only accounting. the real word is trust or fides, which is used in fiduciary.

For the Romans, FIDES was an essential element in the character of a man of public affairs, and a necessary constituent element of all social and political transactions (perhaps = 'good faith'). FIDES meant 'reliablilty', a sense of trust between two parties if a relationship between them was to exist. FIDES was always reciprocal and mutual, and implied both privileges and responsibilities on both sides. In both public and private life the violation of FIDES was considered a serious matter, with both legal and religious consequences. FIDES, in fact, was one of the first of the 'virtues' to be considered an actual divinity at Rome.

http://www.csun.edu/~hcfll004/fides.html