Year 634 (DCXXXIV) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. The denomination 634 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. Events By place Byzantine Empire Arab–Byzantine War: Emperor Heraclius, ill, infirm, and unpopular with the Eastern Orthodox Church, is unable to personally lead the Byzantine army to resist the Muslim conquest of the Levant. He sends his brother Theodore to assemble forces to retake the newly won Muslim territories. Monophysites and Jews throughout Syria welcome the Arab invaders, as they are discontented with Byzantine rule. July 30 – Battle of Ajnadayn: Byzantine forces (90,000 men according to Muslim sources) under Theodore are defeated by the Rashidun Caliphate near Beit Shemesh (modern-day Israel). Heraclius, who is in Emesa, flees to Antioch upon hearing news of the battle's outcome. Europe King Dagobert I is forced by the Austrasian nobles to put his 3-year-old son Sigebert III on the throne, ceding royal power in Austrasia. He frees himself from dependence on Pepin of Landen, and extends his rule over the Bretons (approximate date). Britain Eanfrith of Bernicia and his bodyguard are killed by King Cadwallon of Gwynedd, in an attempt to negotiate peace. Eanfrith's brother Oswald returns from 18 years exile in Dál Riata (modern Scotland), to claim the crown of Northumbria. Battle of Heavenfield: Oswald, possibly accompanied by a force of Scots (or Picts), defeats and kills Cadwallon with a Welsh army near Hexham (northern England). He reunites Deira with Bernicia, and becomes king of Northumbria. Persia Battle of the Bridge: Persian forces (10,000 men) under Bahman Jadhuyih defeat the Muslim Arabs at the Euphrates (near Kufa). The sight of elephants panics the Muslims, and many are killed. Bahman does not pursue the fleeing Arab army. Arabia Battle of Firaz: The Rashidun Arabs (15,000 men) under Khalid ibn al-Walid defeat the combined forces of the Byzantine Empire, Persian Empire and Arab Christians (at least 10 times larger than Khalid's army) in Mesopotamia (Iraq). February 4 – Battle of Dathin: Rashidun forces under Yazid ibn Abi Sufyan defeat the Christian Arabs around Gaza. The Muslim victory is celebrated by the local Jews, who have been a persecuted minority within the Byzantine Empire. The Rashidun Caliphate starts the Islamic conquest of the Byzantine Empire, when