In the Roman inheritance law, until post-classical law, the appointment of an heir on the basis of the rule heredis institutio caput et fundamentum totius testamenti est, was the foundation of the whole will. Heredis institutio was a crucial element of the content of the will and it should be placed in the very beginning as all dispositions placed before it, were void. And remained this way until Justinian law where the above mentioned formalism was annulled. First exceptions of the rule heredis institutio caput et fundamentum totius testament est and the order arising from testamentary dispositions placed therein, can be noticed in classical law, according to the constitution of custody, appointment to inherit by the own slave together with his liberation and disinheritance. Moreover, Roman law, based on the performance of praetors and Cesar law, exceptionally allowed the maintenance if the rest of the testamentary content (demises, trusts, liberations) when the heredis institutio fell or did not lead to inheritance. And so, the acceptance of the heir appointed in a will becomes a sole formality in classical law, and a range of deviations and exceptions appear in the discussed rule Heredis institutio caput et fundamentum totius testamenti est. The Western Roman post – classical practice and Justinian omitted the above mentioned rule totally.