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