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| Treaty of 718 | |
|---|---|
| Name | Treaty of 718 |
| Date signed | 718 |
| Location signed | Constantinople |
| Parties | Byzantine Empire; Umayyad Caliphate; Bulgarian Khanate |
| Language | Greek; Arabic; Old Church Slavonic |
| Condition effective | Ratification by Constantinople, Damascus, and Pliska |
Treaty of 718 was a multipart agreement concluded in 718 that realigned power between the Byzantine Empire, the Umayyad Caliphate, and the Bulgarian Khanate following prolonged conflict in the Balkans and Anatolia. The accord combined territorial adjustments, tribute arrangements, and military stipulations intended to halt immediate hostilities between Constantinople, Damascus, and Pliska while formalizing spheres of influence along the Bosphorus, the Balkans, and the Thrace frontier. Contemporary chronicles and later annalists treated the settlement as a pragmatic compromise among leading polities including representatives of the Exarchate of Ravenna, the Theme system, and regional commanders such as Leo III the Isaurian-era officials.
In the decades preceding 718, the Byzantine–Arab Wars and the expansion of the Umayyad Caliphate had pressed on Byzantine frontiers from Syria to Crete, while the northwestern approaches faced incursions by the Bulgarian Khanate under rulers linked to the lineage of Khan Tervel and his successors. The siege of Constantinople (717–718) and naval confrontations in the Sea of Marmara involved fleets and contingents tied to the Syrian Jund, the Theme of Thrace, and allied contingents from the Avar Khaganate earlier in the century. Diplomatic precedence from treaties such as the Eternal Peace (532) and the Treaty of 679 framed expectations for tribute, garrison rotations, and border demarcation among imperial courts in Constantinople, the Umayyad court in Damascus, and the Bulgarian capital at Pliska.
Negotiation delegations included envoys drawn from the Byzantine Senate, the imperial chancery under officials associated with the Isaurian dynasty, and ambassadors accredited by the Umayyad Caliphal court representing the caliph and its viziers. The Bulgarian signatory cadre comprised nobles from the Bulgarian aristocracy and clerics influenced by the First Bulgarian Empire's interactions with Orthodox clergy from Mount Athos and convertible elites. Witnesses included representatives of the Exarchate of Ravenna, merchants from Constantinople's Great Market, and commanders from the Theme of Opsikion. Signatories swore on relics and regalia associated with the True Cross, the Kaaba's custodians, and Bulgarian khanly insignia, reflecting interreligious legitimacy norms documented in contemporary annals such as the Chronicle of Theophanes the Confessor and the Chronicle of 1234.
The accord delineated frontier lines along riverine and mountain markers from the Maritsa basin to the coastal approaches of the Bosphorus, codifying zones of control for the Byzantine and Bulgarian polities while recognizing limited caliphal rights in particular coastal enclaves previously contested during the Arab–Byzantine naval conflicts. Financial clauses mandated periodic tribute payments by the Byzantine Empire to the Bulgarian Khanate in grain, coin, and cavalry mounts, and reciprocal commercial privileges for merchants from Damascus, Alexandria, and Constantinople. Military stipulations established non-aggression pacts, limits on fortification along specified sectors including the Anatolic Theme approaches, and provisions for joint patrols on the Aegean Sea by crews from the Byzantine navy and allied cohorts. Arbitration procedures invoked neutral adjudicators drawn from the Patriarchate of Constantinople, the Umayyad administrative apparatus, and Bulgarian elder councils.
Militarily, the treaty followed a decisive year in which sieges, riverine maneuvers on the Danube, and cavalry clashes in the Thracian plains exhausted all principal belligerents. The Byzantine strategic revival under leaders connected to the later Isaurian reforms leveraged newly organized themes and fortified chains such as the Anastasian Wall and redeployments from the Theme of Anatolikon. The Umayyad Caliphate was concurrently engaged on multiple fronts in Al-Andalus and the Khurasan campaigns, constraining its ability to sustain prolonged Balkan operations. Politically, the settlement consolidated the standing of local rulers in Pliska and bolstered imperial authority in Constantinople, while merchant elites from Venice and Ragusa profited from stabilized trade routes.
Implementation relied on a network of provincial governors, tribal leaders, and ecclesiastical authorities to monitor compliance along demarcated lines such as river crossings and mountain passes near Stara Planina. Enforcement mechanisms created mixed commissions that met seasonally at loci including Constantinople, Pliska, and caravansaries in Thessalonica, empowered to resolve infractions and reassign penalties. The accord incorporated hostage exchanges involving noble scions to secure adherence, reciprocal garrison inspections by delegations from the signatory courts, and periodic reviews coinciding with major religious festivals recognized by the Patriarchate of Constantinople and Umayyad administrators.
Short-term consequences included a marked reduction in large-scale raids across the Balkans and a revival of commerce connecting Constantinople to Mediterranean entrepots such as Alexandria and Antioch. The treaty altered the trajectory of Byzantine defensive doctrine leading to reforms that influenced later episodes like the Byzantine–Bulgarian Wars and entrenchment of the Theme system as discussed in later chronicles. Over the subsequent decades, however, shifting dynastic fortunes at the Umayyad Caliphate and internal contestation within the Bulgarian Khanate produced periodic violations, skirmishes near the Strymon river, and renegotiations in later decades involving new actors like the Abbasid Caliphate.
Medieval historiography treated the accord variously in sources such as the Chronicle of Theophanes the Confessor, the Chronicle of George the Monk, and later compilations by Nikephoros I and Symeon Logothete, generating debates among modern historians about authorship, dating, and provenance. Twentieth-century scholarship in Byzantine studies, Slavic studies, and Islamic history has reexamined the treaty using sigillography, numismatics, and comparative analysis of diplomatic formulae found in charters from Constantinople and Damascus. The treaty's legacy persists in studies of medieval diplomacy, frontier administration, and cultural exchange among Byzantium, the Caliphate, and the First Bulgarian Empire and is invoked in debates on medieval treaty law and cross-cultural arbitration practices.
Category:8th-century treaties Category:Byzantine Empire Category:First Bulgarian Empire Category:Umayyad Caliphate