At a later time the form of plebeian will developed ( " irs / amentum per aes ci libram " ), and the law of testamentary succession was further modified by the influence of " tile practor ", especially in the direction of recognition of " fideicommissa " similar in some respects to testamentary trusts . " Codicilli ", or informal wills, also came into use and were sufficient for almost every purpose except for appointing an heir.