A few metres east of the famous (now ruined) church of Dormition of the Virgin in Nicaea, where the street Yakup Chelebi is today, there is a mysterious monument, known as Böcek Ayasma (sacred spring of Böcek). It is a vaulted structure with an almost circular ground plan, of internal diameter around 4.5 m and internal height of 3.8 m. It is lower than the level of the street as it is today, and therefore gives the impression of a semisubterranean.

In order to approach the building entrance, one must descend 11 steps from the road surface. The walls are built using rumble or slightly processed stones and mainly, bricks. Plaster has been used as connecting material. The opening of the only entrance is 2.55 high. Over this opening, there is a blind arch made by wide and long bricks. In the center of this arch, there opens a shallow, rectangular recess. A long marble architectural member has been installed as a lintel, during a second phase of the site. Two deep and parallel engravings decorate it. Internally, in the wall of the circular room, in each of the four points of the horizon, there is a niche with a semi-circular crowning. The use of big processed stones emphasizes the contour of the crowning. Flanking the eastern niche, spolia have been installed symmetrically, marble architectural members bearing geometrical and vegetal motifs. One of these bears a great cross. Carefully installed stone slabs cover the floor. In the center of the floor, there is an orifice of square ground plan, having a side length of 0.5 m and a depth of approximately 0.8 m. Almost on the same level with the floor, the four sides of the orifice are marked by four marble plaques. The plaque on the eastern side bears an inscription in greek (possibly dated to the Late Byzantine period) :

"ΠΥΡΓΟΣ ΜΙΧΑΗΛ ΜΕΓΑΛΟΥ ΒΑΣΙΛΕΩΣ ΕΝ Χ(ΡΙΣΤ)Ω ΑΥΤΟΚΡ(ΑΤΟΡΟΣ)".
"Tower of grand basileus Michael, emperor by the grace of God"

Another plate bears a Judaic inscription of the 2^nd century B.C., namely a quotation from the Old Testament. At the northwest side of the wall construction, there is an engraved representation of a Judaic seven branched candelabrum (Menorah). It is, therefore, possible, that architacture material from a Jewish synagogue was used, among other things, in the construction of the building.

The monument in its totality had not been studied and any effort for a chronology remains risky. Assumptions on the use and chronology of the building have been made only within the framework of studies regarding the entire city of Nicaea and its monuments. As an architectural structure, the building has been dated to the 6^th century, according to recent studies.¹ Regarding its use, the Iznik Municipality website mentions that the area “was operating as a baptisterium and later as a sacred spring” (hagiasma). However, M. Restle’ s reservations are possibly correct, when he says “the alleged use of the area as a baptisterium remains doubtful”.² A. B. Yalcin obviously accepts these reservations, since he only mentions the building as “hagiasma” (fonte sacra).³ Likewise, S. Foss believes that in all probability, the building was used as a sacred spring. A more systematic study of the specific monument, in combination with a search for the relationship it might have had with the nearby church of Dormition of Mary, might give a more certain answer to this enigma.