Byzantine–Pisan Treaty of Alliance

Timeline

1. 1108–1110Constantinople · Sea of MarmaraAfter the Treaty of Devol, Alexios needed diplomatic means to compel Antioch to accept its terms and to counterbalance Venice's monopoly in imperial waters. Pisa, expanding its commercial interests in the Eastern Mediterranean after participating in the First Crusade, saw its interests intersect with Byzantium's, and the two sides began negotiating mutual privileges and military cooperation obligations.
2. 1110–1111Constantinople · Sea of MarmaraAlexios issued a chrysobull: Pisan trade tariffs in imperial waters were capped at 4%; they were permitted to worship freely at the Church of Saint Mary in Constantinople and received a stipend of 400 hyperpyra; the emperor promised compensation for Pisan ships wrecked on imperial territory. The Pisan envoys swore to cooperate with Byzantium, not to sell contraband to the empire's enemies, and to acknowledge the emperor's overlordship in the manner of a vassal.
3. 1111–1136Eastern Mediterranean · Eastern MediterraneanThe treaty allowed Pisa to compete with Venice in Byzantine waters and expand its trade with Syria and the Aegean. After 1111, conflict between Pisa and Venice intensified; John II renewed the privileges in 1126 and 1136, and Manuel I confirmed the tariff provisions again in 1170. This alliance is a typical example of Byzantine 'using Italians to check Italians' diplomacy.