The Palazzo Pubblico, the town hall of Siena, stands at the lower end of the steeply sloping Campo, with the Piazza del Mercato at its rear. The building project was initiated in the 1280s, when it was decided to combine in one building the Customs offices, the Mint and the Council offices, together with the residence of the Podesta. The new palazzo was designed to face the Campo, unlike the old Mint, which had overlooked the Val di Montone. The structure consisted of a central tower block of slightly trapezoidal plan. The ground-floor facade was faced in stone, with four doors of a characteristic Sienese type (a shallow arch contained within a pointed arch). Above this were two storeys faced in brick, each with four three-light windows, and the whole was crowned with battlements. In 1304 the tower was extended on the rear, market side and heightened by one storey, with three two-light windows at the front. Between 1307 and 1310 the two-storey side wings were built, canted slightly in relation to the central block, and each with three three-light windows. In 1325, the foundations were laid for the brick tower (the Torre del Mangia) that rises 88 m above the Palazzo. Its construction was begun in 1339 by the Perugian brothers Muccio and Francesco di Rinaldo under the supervision of Agostino di Giovanni. The tower was finished in 1348 with a belfry of travertine marble, which is traditionally thought to have been designed by the painter Lippo Memmi. In 1354 the Cappella di Piazza was built at the base of the tower; in 1468-1470 its porch received a Renaissance canopy by Antonio Federighi. In 1680, perhaps under the direction of the architect Giovanni Battista Piccolomini (1623-1697), a storey was added to each of the lateral wings of the Palazzo Pubblico, designed to correspond stylistically with the rest of the building.