The Abbey of Saint Galgano was a Cistercian Monastery founded in the valley of the river Merse between the towns of Chiusdino and Monticiano, in the province of Siena, region of Tuscany, Italy.

Nearby are the chapel or Eremo or Rotonda di Montesiepi (1185), the tomb of Saint Galgano and the purported site of his death in 1181, a sword said to have been driven into a stone by Galgano,[1][2] and a chapel with frescoes by Ambrogio Lorenzetti.

Monks from the abbey routinely served as Camarlinghi di Biccherna,[3] i.e. high magistrates of the main financial institution of the republic.

[4] However within a century, the republic failed to protect it from roving condottieri, and John Hawkwood and his men despoiled the monastery beginning in 1363.

The Rotonda chapel was restored in 1924 and retains its peculiar medieval shape, similar to earlier Ancient Roman mausoleums.