South of the Rotunda was the triumphal arch (known today as “Kamara”), probably built by the city of Thessaloniki between 298 and 305 AD to commemorate Galerius’ victorious campaign against the Persians. It is one of the 15 Paleochristian and Byzantine Monuments of Thessaloniki that were included in the UNESCO World Heritage List in 1988.
In its final form, the structure consisted of eight piers arranged in two parallel rows, four in each row. Between the piers were created three arched openings, of which the central one was wider and higher than the other two. The four central piers, which carried marble slabs with relief decoration, were larger than the outer piers and were connected by semi-circular arches supporting a dome.
Today only three of the eight original piers are preserved (the position of the destroyed central piers on the east is indicated on the sidewalk of Egnatia Street by a different paving), of which two carry reliefs depicting scenes from the Romans’ victorious campaigns against the Persians in 297 AD, in addition to symbolic images propagandizing Galerius’ military might and the power of Tetrarchy.
The triumphal arch was built at the intersection of two streets. One of these was the linear “processional way” with porticoes starting from the arch’s north side and concluding at the south gate to the Rotunda’s enclosure; the other was a main avenue, the Roman decumanus maximus, Mesi or “Leoforos” as it was called by the Byzantines, which traversed the city from west-east. This avenue, of which remains have been found beneath the street paving and north of the modern-day Egnatia Street, passed directly between the main piers of the triumphal arch and concluded at the Kassandreotiki (Cassandrian) Gate of the eastern wall (at Syntrivani Square). In this section, the street had a width of about ten meters and was flanked on either side by porticoes which ended at the openings of the small piers of the Arch. Shops opened up behind and along the length of the porticoes, which were 5.50 meters wide.
Directly abutting on the smaller southern piers of the Arch was a large rectangular vestibule (42.70 x 17.65m.), remains of which were found beneath the paving of Egnatia Street. The floor of the vestibule was 0.90 meter below that of the porticoes, and it had a mosaic paving featuring geometric and vegetal motifs. There was an opening (approximately 18 m.) in its southern wall from which a monumental marble staircase (4 m. in length, 11 stairs) began. According to some researchers, it led to a large city square through which one could enter the Hippodrome, which lay to its east.
South of the square, the so-called “Apsidal Hall” of the complex was built. Today its remains are visible at the archaeological site on Dimitriou Gounari Street.