Piazza delle Erbe may not be much larger than a handkerchief yet it is one of the most picturesque corners of Mantova. Not only is this medieval square bordered by buildings of various styles, it was once the seat of city government and has been a center of commerce since time immemorial. Palazzo del Podesta, at the square's north end, housed the city hall in the Late Middle Ages. Palazzo della Ragione served as two things when built in 1227. Justice was dispensed in its upper floor salon. Shops and eateries filled the portico, much like today. Both buildings were given a facelift in the Renaissance. Palazzo del Podesta got double pier windows and a new doorway. Palazzo della Ragione got a watchtower. Casa del Mercante, built in 1455, was home to one of the city's wealthiest merchants. The architectural style is a mix of Late Gothic and Venetian. Rotonda di San Lorenzo, the oldest church in Mantova, occupies a central place in Piazza Erbe. Built by Matilde di Canossa in 1082, this simple round Roman church boasts traces of Byzantine frescoes and sits at the original level of the square.