Treaty of San Germano is signed at San Germano between Holy Roman Emperor Frederick II and Pope Gregory IX. A Dominican named Guala is responsible for the negotiations.

The Treaty of San Germano was signed on 23 July 1230 at San Germano, present-day Cassino, ending the War of the Keys that had begun in 1228. The parties were Pope Gregory IX and Frederick II, king of Sicily and Holy Roman emperor. On 28 August at Ceprano, the peace was finalized with the readmission of the excommunicated Frederick into the church.

Cassino is a comune in the province of Frosinone at the southern end of the region of Lazio. It's the last city of the Latin Valley.