The Battle of Fahl, also known as the Battle of the Marshes and the Battle of Beisan, was a major battle in the Muslim conquest of Byzantine Syria fought by the Arab troops of the Rashidun Caliphate and Byzantine forces at or near Pella (Fahl) and nearby Scythopolis (Beisan), both in the Jordan Valley, in December 634 or January 635.

The Muslim conquest of the Levant, or Arab conquest of Syria, was a 634–638 CE invasion of Byzantine Syria by the Rashidun Caliphate. A part of the wider Arab-Byzantine Wars, the Levant was brought under Arab Muslim rule and developed into the provincial region of Bilad al-Sham. Clashes between the Arabs and Byzantines on the southern Levantine borders of the Byzantine Empire had occurred during the lifetime of Muhammad, with the Battle of Muʿtah in 629 CE. However, the actual conquest did not begin until 634, two years after Muhammad's death. It was led by the first two Rashidun caliphs who succeeded Muhammad: Abu Bakr and Umar ibn al-Khattab. During this time, Khalid ibn al-Walid was the most important leader of the Rashidun army.