Since the medieval era a commercial area has been present in the southeastern part of the city close to piazza Mercantile, from which the "ruga Frangigena" began, the route pilgrims took which led them to the Basilica di Saint Nicholas.
In the heart of the square, in front of the palazzo Sedile a stretch of medieval pavement was found (made from limestone blocks) that, thanks to the discovery of coins belonging to the principality of Achaia, has been possible to date it to the first half of the fourteenth century.
The piazza, close to the port, to which it was connected by a fortified structure placed at the entrance of the pier (the tower S. Antonio), was home to the city government from at least the middle of the fifteenth century, becoming a popular urban meeting point. Subject to the urban renewal program implemented under the Sforzas, the piazza was subjected to an overall reorganization at the beginning of the seventeenth century, following a dramatic event that occurred in 1601: a fire swept through some houses that occupied a triangular area next to the palazzo Sedile and finished at the arsenal adjoining the palazzo Sedile, which resulted in a violent explosion. The palazzo Sedile was rebuilt quickly and was given a bell tower that housed a German made clock which even showed quarters of an hour. In 1612 a new carriageway door that connected the piazza to the harbor via the adjoining piazza Ferrarese was opened; the reorganization further contributed to consolidate it as the business centre for the citizens.
At the beginning of the 9th century the university's headquarters moved to the "Ruga Fragigena", which has since taken the name of strada Palazzo di Città, while the former palazzo Sedile was used as a theatre. Piazza Mercantile still retained the role of the meeting point, used for festivals, ceremonies and public entertainment, while health and hygiene requirements became increasingly important forcing the selling of food in to the nearby piazza Ferrarese that after the demolition of the walls and the door became the specialised marketplace.
Throughout the 19th century, with the building of the commercial port on the opposite side of the city, the piazza lost its historical role as the centre of life for the citizens of Bari, being slowly replaced by Corso Vittorio Emanuele (already Ferdinandeo), where the most important public buildings and meeting points could be found.