This loggia overlooks the ancient stretch of the Via Francigena and it was probably built to give a strong image, in the eyes of passers-by, of the merchant power of Siena.
In 1417 Sano di Matteo designed the Loggia della Mercanzia as an extension of the Palazzo della Mercanzia, which overlooks Piazza del Campo. The work was completed in 1444, it has a Gothic-Renaissance style and five statues set in the pillars that support the arches: they represent St. Peter, St. Paul, St. Savinus, St. Ansanus and St. Victor, the first two are sculptures by Vecchietta and the other three, ancient protectors of the city, by Antonio Federighi. Federighi himself created one of the two marble benches on the right at floor level; the other, on the left, is a work of Urbano da Cortona. The vaults of the loggia were frescoed by Pastorino dei Pastorini, as far as the left one is concerned, and the other two by Lorenzo Brazzi in the years 1549-1553.
Since 1764 it has been the seat of the Circolo degli Uniti, the oldest club of nobles in Italian history, founded in 1657.