The structure was an octopylon (eight-pillared gateway) forming a triple arch that was built of a rubble masonry core faced first with brick and then with marble panels with sculptural relief. The central arched opening was 9.7 m wide and 12.5 m high, and the secondary openings on other side were 4.8 m wide and 6.5 m high. The central arch spanned the portion of the Via Egnatia (primary Roman road from Dyrrhacium to Byzantium) that passed through the city as a decumanus (east-west major street).