Castello Mediceo, Renaissance fort in Sansepolcro, Italy.

Castello Mediceo, also called Fortezza di Sansepolcro, is a Renaissance fortification built into a corner of the town walls. It has an almost square plan with four heart-shaped corner bastions of different sizes, and its lower masonry is attributed to Giuliano da Sangallo while the upper sections were added later.

Giuliano da Sangallo was commissioned around 1500 by Florence's Dieci di Balia, and work began between late 1502 and early 1503. He built over a 14th-century Malatesta fortified borgo enclosing the Rocca di Sant'Angelo, itself raised on a Roman tower. Under the Lorraine the armaments were moved to Florence's Fortezza da Basso; in 1754 the fortress was leased to Francesco Alberti, passed to the Collacchioni in 1842, and became private property in 1904.

The four corner bastions carry the names Belvedere, Santa Maria, San Casciano and San Leo; the Belvedere is the largest. The San Leo bastion has a circular shaft running vertically through it, a chimney for the smoke of the artillery mounted on its floors. The fortress became a private farm in the 19th century, and the carriage gate dates from that period.

The fortress is private property, held by the Tosi family since 1916, so it is not open as a public monument; views of the square plan and the four heart-shaped bastions are best from outside and from aerial photographs. The inner floor lies over two metres above the outside road, and the moat is largely filled in.

The San Leo bastion hides a circular shaft running vertically through the whole structure, a flue for the smoke of the artillery mounted on its floors; its size suggests large-calibre guns, probably installed after Sangallo's work. The third gate, tucked behind the San Leo bastion's ear, still shows it was fitted with a drawbridge and predates the surrounding fortification.