The Piazza dei Leoni is one of the most famous and characteristic spaces of the ancient city, enclosed between the apses of the Cathedral, the row of medieval Costa houses grouped around the tower and the sober facade of the Costa palace, later del Carretto di Balestrino and from 1954 , by donation of Domenico del Carretto di Balestrino, residence of the bishop of Albenga. The row of medieval houses on the north side has different building types (14th-15th century); The tower is the only one in the city to have a base in large Finale stone ashlars, with a pointed arched door; the top of the brick facing is decorated with three cornices of hanging arches, an evident imitation of the decoration of the Cathedral bell tower, and the crowning with Ghibelline battlements. The medieval house next to the tower has, on the back facing Via Pertinace, a large loggia with pointed arches, now buffered. In the Middle Ages, the square was the seat of the liveliest market in the city, the forum callegariorum or scoferiorum, where shoemakers and leather tanners worked and exhibited their artifacts: it was a very important handicraft due to the existence of numerous tanneries outside the walls. along the river. A lively center of commerce and trade, the square also housed, in one corner, the fig market (forum ficuum), while in the ancient bishop's palace that closed the square on the west side there were the vintners' shops (forum wines).
After the Middle Ages, the square was partly occupied by the construction (1519-1525) of the Costa Palace which is the first example in the city of a sixteenth-century building with a large staircase and two noble floors. The ground floor atrium houses some important epigraphic testimonies: in particular the plaque commemorating the reconstruction of the city due to general Flavio Costanzo, later emperor Constantius III, husband of Galla Placidia, in elegiac couplets, attributed to Rutilio Namaziano and dated around 417 AD On the second noble floor, the large reception hall has an important wooden coffered ceiling, decorated with the heads of Roman emperors, garlands of flowers and foliage and coats of arms; in the band below, decoration with parades of horses, mythical characters and even coats of arms, the work of the local painter Bernardo Reubado. Until the early 1950s, the hall had walls covered with paintings of many sizes, an important collection unfortunately dispersed after the death of the last Del Carretto.
The square takes its name from the three stone lions that decorate it, almost guarding the palace, sent from Rome by Ottavio Costa and placed here by his brother Abbot Alessandro in 1608.