The remains of a Late Antique hypogeum are located in the garden of the Bakirköy Psychiatric Hospital. Bakirköy, once a Constantinopolitan suburb known as the Hebdomon, was important as the site where many emperors were proclaimed or began their triumphal processions. The mausoleum of Basil II was also located at the Church of St. John the Evangelist in the Hebdomon, rather than the customary Church of the Holy Apostles. The remains of a circular mausoleum along with six sarcophagi were discovered at Bakirköy in 1914. While initially identified as the mausoleum of Basil II in the Constantinopolitan suburb known as the Hebdomon, it likely dates to the 5th century. Another sarcophagus in the area of the Hebdomon was also associated with Basil II, though this is far from certain.

A circular hypogeum was discovered at Bakirköy in 1914 during the construction of barracks, but was not excavated until after World War I was over. Excavations, under the guidance of Makrides, began when the barracks were taken over by French occupation forces. While the excavations were incomplete when the French forces withdrew, it was initially claimed that this was the tomb of Basil II. Later research, though, demonstrated that the hypogeum was an earlier structure, probably contemporary with the fifth-century sarcophagi it housed. Instead he argued that his resting place was a white marble sarcophagus found near the ruins of St. John Prodomos in Bakirköy. The sarcophagus, which had been converted into a water fountain in the Ottoman era, disappeared sometime after 1939.

The circular hypogeum has a diameter of around 15 meters and had a cupola resting on four barrel vaults and four pendentives. It was divided into four sections in the form of a cross and had a circular corridor. Each of these sections took the form of a massive triangular brick pillar connected to the inner wall of the hypogeum. All four walls of these sections had an arched niche that to house a sarcophagus. Six sarcophagi, which were discovered in the eight niches, were number in Greek. One of these sarcophagi, which disappeared by 1922, contained three skeletons and had an inscription declaring “Here lies the blessed Epiphanios”. An additional sarcophagus was buried under the western section. It was carved from a single large block of white Proconnesian marble and had two large marble lids, one atop the other, and contained a single skeleton as well as an earthenware phial and several small lead objects. The sarcophagus had a sculpted decoration of a medallion and ivy leaf on all four sides. On the long sides there are crosses after the ivy leaves, as was typical in the 5th century.