Built into a small space (an early guardhouse) within the ancient Golden Gate of Diocletian's northern wall,[2][3] it is one of the oldest churches in the city.

"Hail Father Martin, allow us to worship you from the bottom of our soul and heart in this small cavern".In identifying Dominic, Bulić dated the inscription to the ninth century and the region of Trpimir I.

It seems the (knez) chaplain Dominic renovated the former guardhouse into the first Christian church in the city dedicated to the Virgin Mary, Saint Gregory I and St. Martin of Tours (the father of western monasticism).

On 4 March 852 Trpimir issued a charter in Biaći (in loco Byaci dicitur) in the Latin language, confirming Mislav's donations to the Archbishopric in Split.

The northern gate of the Palace had been conceived as the main entrance, and so it had been elaborately decorated with statues of Emperor Diocletian and his co-regent Maximian in the upper row of the niches, and with a sculpture of an eagle (a symbol of Jupiter), between the two.

On the top of the wall, there have been four pedestals preserved until the present day (while there were five of them on the drawings from the 18th century) that could have been used as a supporting base for statues, but it is unlikely to believe that the imperial figures would have been repeated twice on the same façade.

[11] On the altar wall, the only one preserved in situ in Dalmatia, there is an inscription with the dedication to the patronage of the Virgin Mary, St. Gregory the Pope and Blessed Martin.

[12] The Byzantine stage, probably built in the 9th century, belongs to the barrel vault, with an altar in the apse with a carved cross of early Christian denominations and a small trance set in the middle of large, buried antique openings on the southern wall.