It is acknowledged that classical Roman inheritance law was "highly complicated and to a large extent perplexedly entangled". Modern development The codicil remained a distinct entity to a will (testament) to varying degrees throughout the Roman-influenced legal world. The concept of heredis institutio (a will requires an heir) was part of the jus commune up until modern times. In the United States, a codicil is a document that changes an existing will. Amendments made by a codicil may alter, explain, add to, subtract from, or confirm – and otherwise amend a will in any other way, minor or major, short of complete revocation. It is subject to the same formal requirements as a will. References Wills and trusts Legal documents