The unique architectural and historical ensemble around the eastern gate of the Acropolis fortress wall is one of the symbols of Plovdiv. 

There has been a gate since ancient times there. Below the level of the street pavement (cobblestone) there are foundations from the Roman period (probably from the 2nd century AD). The presence of topographic continuity on the Three Hills can also be seen here. The present appearance of the gate is determined by the dominant medieval alteration of 11-13th century. Above the outer arch can be seen specific construction, which surrounds each stone with pieces of red brick, cemented with plaster – something typical for the Bulgarian construction mastery of the period of the Second Bulgarian Empire. The outdoor quadrangular tower under the altar of St. Konstantin and Elena Church is also assigned to this ensemble. It served as a crypt (ossuary) for many years. Further to the south of the church complex is visible a large section of the fortified wall with a circular tower from 5-6th century during the reign of Justinian the Great. A Turkish garrison was established here in the 14th century with the Ottoman invasion, and then Hisar Gate, being part of the fortification system of the Acropolis, lost its importance. Later, around 17-18th century, the houses of the rich merchants’ class were built here.