The antique amphitheater of Serdica was found in 2004 in Budapest Street eastern from the Serdica city, outside the city walls. It is dated back as far as II-III century. The remains of the Arena itself that were excavated were five radial walls each 0.55 wide and 2.30 long build of bricks and mortar. They reach semi-round wall with the same construction. These remains are supposed to belong to earlier time period probably Roman Theater. It is considered that the Roman Theater was demolished around III century and the new Amphitheater was build. The semi- round construction is covered with river stones - they functioned as a base for the next construction level of stone plates and bricks. There was found one more wall - 0.7 wide and 7 meters long that expands north-south.
In 2005 most of the curved wall surrounding the Arena was uncovered. The inner face is constructed of brick masonry and the outer of stone one. In 2006 the whole Arena was excavated, but part of it and the entrance of the antique theatre remained under the newly build hotel. The tribunes located in the south part of the structure unit are well preserved and the impressive part of the curved wall construction supporting the stands is visible. The masonry technique is opus mixtum and its width is 2.20 meters. The founded arches are examined in situ. Eighteen seats were found fallen on the Arena. Amphitheater was probably constructed during the reign of Diocletian and Constantine the Great, when Serdica became a capital of the Inner Dacia province. Its closing as a pagan building was probably in IV century.
The Roman Theatre and the later antique Amphitheatre are the largest civic buildings that have been found till now as a remains of the ancient Ulpia Serdica city. Part of the remains are now exposed at the ground level of hotel Arena di Serdica.