The church, which is one of the oldest and less known churches in Athens, is dedicated to Panagia Pantanassa. It is celebrated on the 15th of August, the day of the Assumption of the Virgin Mary. It is located in Monastiraki Square, which is named after it.

The church is referred to as Big Monastery in a post Byzantine sigillium of 1678 and it is thus named during these years. Furthermore, in the same document it is mentioned that during the period of the Frankish rule it was annexed as a men’s monastery to Kaisariani Monastery. During the period of the sigillium the monastery functioned as a convent. From 1690 onwards the church became parish, same as the Kaisariani Monastery. From the revolution onwards, the church was no longer called Big Monastery but Mikromonastiro (Small Monastery) or Monastiraki. The monastery cells used to be in the location of today’s Square, while the whole area was full of small shops, many of which can still be found in the neighboring Pandrosos Street.

The church is a barrel-vaulted basilica, namely a church type characteristic of the transition from the early Christian basilica to the cross-in-square church. In general, it signifies the transition from Late Antiquity to the Byzantine and Medieval World.

The wall paintings are more recent.

The church has undergone many modifications. Characteristic is the bell-tower, which is a more recent construction and annex.

According to Orlandos, the church is dated to the 10th century. However, based on its masonry Sotiriou has dated it to the 7th – 8th century, while Wulff to the 8th – 9th century like all the barrel-vaulted basilicas of Athens. Xyngopoulos has dated the church to the 10th century, whereas Millet to the 11th – 12th century based on its capitals.