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.
The negotiations for the treaty, initiated by Frederick, began in November 1229. The Lombard League, an ally of Gregory, objected to the process. The intercession of major German princes, especially Duke Leopold VI of Austria and Grand Master Hermann von Salza, was necessary to move things forward. The most important negotiator on the papal side was Cardinal Thomas of Capua, although Gregory's actual representative at the signing was Guala de Roniis.
In territorial terms, the treaty essentially restored the status quo ante bellum. Frederick recognized the Papal State and Gregory recognized Frederick as king of Sicily and emperor unimpaired. A general amnesty was issued. The biggest concession was Frederick's surrender of his special rights over the church in Sicily. Nevertheless, the treaty has often been regarded as a victory for the emperor.
Background
The causes of the War of the Keys were Frederick's failure to lead the Sixth Crusade on the schedule he had agreed and his alleged violations of ecclesiastical rights, especially in the Papal State in central Italy. In October 1227, Gregory excommunicated Frederick. In June 1228, Frederick left on the Sixth Crusade without Gregory's approval. During his absence, his lieutenants, with various excuses, invaded the Papal State. Gregory absolved his subjects of their oaths of allegiance and launched a war into the dispute central Italian territory and into southern Italy, with the goal of confiscating the Kingdom of Sicily.
The papal forces cleared the Papal States of imperial troops, but their advance in Sicily was slow and finances were short. Frederick, having successfully recovered Jerusalem on crusade, returned to Italy and quickly threw the papal forces back on their own territory. Several sieges were still grinding on when peace feelers were first extended by Frederick.
Negotiations
The initiative for peace had not come from Gregory, but from Frederick and probably also some members of the college of cardinals. In October 1229, the Roman Senate bypassed Gregory and opened negotiations with Frederick. On 4 November, Cardinal Thomas of Capua arrived in Aquino to open negotiations on behalf of the pope. On 10 November, Gregory gave Cardinal John of Colonna the power to absolve Frederick of his excommunication. The same day he informed his ally, the Lombard League, that he had opened negotiations. On 11 November, he wrote to Frederick formally expressing his desire to accept him back into the church and make peace.
Thomas and John were the main papal negotiators. The letters and registers of Thomas are an important source for the process. Even so, he frequently refers to information that could only be shared orally. Frederick's negotiators were the Teutonic grand master Hermann von Salza, Archbishop Lando of Reggio and Archbishop Marinus of Bari. The negotiations were protracted, with embassies moving back and forth between the papal and imperial courts. Rains, however, left the roads in a poor state, impeding travel.
In February 1230, the Lombard League object to the negotiations. In March, Thomas informed Gregory that Frederick might give him what he wanted if he only lifted the excommunication immediately. In the end, the German princes intervened on behalf of Frederick to save the negotiations. In April 1230, however, to prevent him from taking part in the negotiations, Gregory renewed the excommunication of Rainald of Urslingen, who had led the invasion of the Papal States.
In May 1230, the papal representatives were prepared to lift Frederick's excommunication if the emperor only recognized papal possession of Gaeta and Sant'Agata dei Goti. He refused. A formula acceptable to both parties was finally agreed on 9 July.
Terms
According to the terms of the peace, Frederick's excommunication would be lifted and all other papal acts against him canceled. A general amnesty was to be issued to those who had supported the pope. Exiles were permitted to return. The properties of the Templars and Hospitallers that Frederick had confiscated were to be returned, as were any lands he had seized from the Roman church. Frederick surrendered his traditional legatine authority over the Sicilian church, agreeing to free ecclesiastical elections and exempting the clergy from secular courts, taxes and tallages.