Palazzo dei Diavoli, Brick palace outside Porta Camollia in Siena, Italy.

The Palazzo dei Diavoli is a brick, castle-like building outside Siena's walls, between Viale Cavour and Via Fiorentina near Porta Camollia. Its oldest section dates to the 14th century; it was later raised and given a cylindrical tower, and in 1460 it was enlarged with a chapel dedicated to Santa Maria degli Angeli, now an oratory, attributed by some to Antonio Federighi. Much of the present structure comes from 19th-century rebuilding.

The palace was originally built in the 14th century as a residence for the Turchi family and bore the name Turcorum Palatium. Over generations, it passed to the Buonsignori family, linking the building to successive noble households through Siena's medieval period.

The palace carries a local legend from 1526 when strange lights and sounds were reported from its windows, giving rise to its present name among Sienese residents.

The palace stands outside Porta Camollia, between Viale Cavour and Via Fiorentina, on the north-western edge of Siena's historic centre. The chapel of Santa Maria degli Angeli, added in 1460, is now an oratory rather than a functioning prayer hall. The present building owes much of its castle-like look to 19th-century reconstructions.

The palace earned its devilish name following reports of mysterious phenomena around 1526 that quickly captured the local imagination. These strange happenings transformed an ordinary noble residence into a local curiosity that survives in memory to this day.