General idea of the Roman law as the basis of the contemporary Croatian legal system is analysed in concreto in this paper through a comparison of the Roman law fideicommissum and the legacies regulated by the provisions of the Succession Act. It is first shown how the concept of singular succession mortis causa appeared and developed in Roman law, as opposed to the appointment of heirs and the universal succession. Namely, while the heir as an universal successor succeeded into a legal position of the deceased, the legatee could obtain a benefit arising out of legacy without being responsible for the debts of the succession. In Roman law, the singular succession was realized in two forms – legatum (legacy) and fideicommissum (trust), distinguished on the formal grounds. Trust emerged as an appropriate alternative to the formal legacy (legatum) and it was often used as a way of circumventing legal restrictions with regard to the passive testamentary capacity. Moreover, it became common practice that testator, with the trust provisions, intended the whole or a large part of the estate to the third party (legatee, beneficiary under the trust) and left the appointed heir nothing but the empty title of heir and liability for the debts of the estate. In order to protect the interests of the heirs and at the same time to preserve the legal effect produced by legacies and trusts, Roman law firstly restricted disposal by legacies, and then by trusts (SC Trebellianum, SC Pegasianum). Finally, a functional balance between universal succession and singular succession mortis causa was established in Justinian’s law. Contemporary Croatian law also provides for the legacy which was unquestionably influenced by the Roman legal tradition. Although the law in force does not allow for the use of special forms of fideicommissary relations (fideicommissary substitution, family trust), while the institution itself bears the name of legatum, it is pointed, through the analysis of Succession Act provisions, that a number of features of legacy today correspond to the features of the Roman trust (fideicommissum).