The baptistery of the city of Split on the eastern coast of the Adriatic in the IX-XI centuries was built in the small temple of the Diocletian's palace, and in the XIII century a font of 12 marble slabs appeared in it, six of which are covered with carvings; the rest of the plates are the spolias of antique sarcophagi and their reliefs are cut out. As a result of many years of research of the monument, all scientists agree that the plates with carvings were taken from the altar barrier of either the Split cathedral of St. Domnius (the former mausoleum of Diocletian), or the church of St. Peter and Moses in Solin. Versions of the identification of the figures on the slab with the image of the ruler on the throne, the figure standing next to and the figure lying below make up two large groups: the sitting figure is either Christ or a some king. Most researchers are inclined to two options: Croatian king Peter Kreshimir IV (1058-1074) or king Dimitar Zvonimir (1076-1089). The details of the subsequent existence of the monument are very interesting: in the hands of the standing figure there was previously an object, most likely a scroll, subsequently removed, and the inscription on the upper field of the slab was erased. In addition, the historical circumstances of the epoch are analyzed, including the weakening of Byzantine influence in the region in the XI century with the strengthening of western influence, which led to liturgical changes reflected in the architecture. The stylistic features of the monument make it possible to attract a number of regional analogies.