Career
His scientific activities include research and publication of medieval sources, research of the oldest settlements in Slovakia, medieval towns, history of Great Moravia, Christianisation of Slovakia and of the Kingdom of Hungary and the oldest history of the Bishopric of Nitra. He worked in leading position at various scientific institutions like Institute of History of the Slovak Academy of Sciences (SAS), Slovak Society for the History, Scientific Board for Historical Sciences, Trnava University in Trnava, Department of the History at Matica slovenská and others In 1960"s he also worked at the research institute of SAS in Budapest, he was the secretary of the Czechoslovak section of the joined Czechoslovakian-Slovak-Hungarian historical commission (1960 – 1965, 1971 – 1983) and the secretary of board of experts at the commission on the sharing of the cultural heritage with the Hungarian People"s Republic (1965 – 1968).