Standing on top of a late Roman church , the cathedral , reconstructed in the 1970s and 1980s , follow a cross @-@ domed plan with a bell tower and a triple apse . Richly decorated on both the exterior and interior , its internal walls now feature modern frescoes , the presence of which have meant that it have not been reconsecrated . Though not active as a Christian place of worship , it have been open for visitors since 1985 .