The Arch and the Tomb of Galerius are neighboring monuments in the city of Thessaloniki. The Tomb of Galerius is better known as the Rotunda, the Church of Agios Georgios or (in English) the Rotunda of St. George. The Arch of Galerius was built in 305 AD, to celebrate the definitive triumph of the Emperor over the Persians.. The whole structure consisted of 4 main pillars and 2 smaller ones on each side, the former supporting a central dome. Through the latter, a connection to the Galerius Palace (to the south) and to the Rotunda (to the north) was possible. Today, only a part of the monument still stands and there is no information on the period or the circumstances under which the rest of the arch was destroyed. The Arch of Galerius belongs to the Galerian group of buildings, in the SE part of the historical center of Thessaloniki. From the original triumphal arch only three pillars and a part of the brick ma-sonry above are preserved to the present day. The two main pillars are covered with sculpted marble slabs, which narrate the wars of Galerius against the Persians. The central arched opening is 9.7 m wide and 12.5 m high and the secondary 4.85 m and 6.5 m respectively. About 150 m northeast of the Arch of Galerius is the Tomb of Galerius, now the Greek Orthodox Church of Agios Giorgios, better known as the Church of the Rotonda (or simply The Rotonda). The cylindrical structure was built in 306 on the orders of Galerius, who intended it to be his mausoleum. After Galerius's death in 311 (he was buried at Gamzigrad / Felix Romuliana near Zajecar, Serbia), however, it stood empty until the Emperor Constantine I ordered it converted into a Christian church. The building was a church for over 1200 years until the city fell to the Ottomans. In 1590 it was then converted into a mosque, the Mosque of Suleyman Hortaji Effendi, and a minaret was added to the structure. It remained a mosque until 1912, when the Greeks captured the city during the Balkan War. It was then formally reconverted to a church, but the minaret was retained. The Rotonda is the oldest of Thessaloniki's churches, and some publications in Greece claim that it is the oldest Christian church in the world, although there are a number of other claimants to that title. It is certainly the most important surviving example of a church from the early Christian period of the Greek-speaking part of the Roman Empire.