He was actively engaged in field research of the medieval cultural and historical monuments, especially murals and Glagoliticepigraphy in Istria, northern Croatian Littoral and Kvarner islands. He discovered and analyzed medieval frescoes in sixty locales in Istria (Istarske freske, 1963; Vincent iz Kastva, 1992). He led archaeological excavations of the Church of St. Lucy, Jurandvor on the island of Krk, as well as the conservation effort of the complex St. Mary's in Osor. In his book Glagoljski natpisi (Glagolitic inscriptions, 1982) he collected paleographic and archaeological descriptions of all known Glagolitic inscriptions, more than 500 of them, which were created during the 11-13th century. He personally discovered more than half of them, mostly in Istria and Kvarner. He found and described the Roč Glagolitic abecedarium, Hum inscription, was the first to decode Valun tablet, Grdosel fragment, Supetar fragment, and contributed to the interpretation of Baška tablet as a left altar partition. His reconstruction of the text of the Baška tablet is the most widely accepted version today.[1]