fidejussors

Very often other persons, called fidejussors or sureties, are bound for the promisor, being taken by promises as additional security.

The Institutes of Justinian John Baron Moyle 1891

8 It is to be observed that in the stipulations of fidejussors the general rule is that whatever is stated in writing to have been done is taken to have really been done; and, accordingly, it is settled law that if a man signs his name to a paper stating that he became a fidejussor, all formalities are presumed to have been duly observed.

The Institutes of Justinian John Baron Moyle 1891