San Pietro in Palazzuolo, Benedictine monastery ruins in Monteverdi Marittimo, Italy.

San Pietro in Palazzuolo is a Benedictine monastery ruin in Monteverdi Marittimo in Tuscany, with walls that still reveal parts of its original layout. The remains show alternating layers of stone and brick, with portions of the left flank and transept still visible.

Founded in 754 by the Lombard noble Walfredo, son of the gastald of Pisa Ratchausi, with investiture from King Astolfo, the monastery stood on the site of a Roman villa and a small temple of the goddess Bellona. It gained importance in the 11th century, was moved to Poggio Badia around 1179, became Vallombrosan in 1298, and was abandoned in 1561 when the monks transferred to Monteverdi castle.

The monastery was entrusted to the Vallombrosans in 1298, and the monks left in 1561 for a hospice inside the castle of Monteverdi, keeping the title of San Pietro. That small house, served by two or three monks from Vallombrosa, is documented until 1781.

The ruins stand on the Palazzuolo hill at Poggio a Badia, in the municipality of Monteverdi Marittimo. The surviving left flank and transept are built of alberese blocks alternating with brick bands on the right side. The site is abandoned and unroofed, so paths are rough; wear sturdy shoes and allow time to walk the grounds.

Granite columns and marble fragments from the Lombard period were discovered near Badivecchia and are now displayed in the Monteverdi Marittimo museum. These finds reveal the site's connections to both its Roman and medieval past.