August 15, AD 636

Battle of the Yarmuk

Rashidun forces defeat the Byzantine field army at Yarmouk

The famous six-day tactical epic rests largely on accounts written generations after the soldiers were dead; one short Syriac notice fixes the disaster to 20 August 636.

August 636: the counterstroke that failed

In August 636 a major Byzantine force under commanders including Theodore Trithurios and the Armenian general Vahan confronted the concentrated Muslim armies near the Yarmouk in southern Byzantine Syria. Early Muslim occupation of Damascus and Homs had threatened the heart of the province, and Heraclius concentrated the maximum troops available for a counteroffensive.

The engagement ended in an overwhelming Muslim victory and the destruction or dispersal of the army sent to recover Syria.

What can and cannot be dated

A Syriac chronological fragment dates the Byzantine gathering and defeat to 20 August 636, matching one strand of later Islamic chronology. Fred Donner cautions that the fragment's own date cannot be established, so it may depend on that same later chronology.

The traditional six-day span of 15–20 August is widely repeated, but the day-by-day narrative comes from much later sources — as do the stories of soldiers chained together, a single bridge of escape, or a dust storm deciding the outcome.

Numbers, and what followed

Army sizes are contested rather than known: Donner estimates 20,000–40,000 Muslim fighting men, an academic review reports Walter Kaegi's estimate of 15,000–20,000 Byzantines, and al-Baladhuri's later account gives 24,000 on the Muslim side.

The victorious army retained control of the Syrian interior while Byzantine survivors withdrew northward. Heraclius's government now lacked the means to reconquer the interior immediately — though northern cities and coastal strongholds still had to be taken.

Sources

Researched 23 Aug 2026 5 sources 3 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~0636-08-20.

What the sources leave uncertain

The traditional six-day span of 15–20 August is widely repeated, but the earliest usable evidence securely supports, at most, a decisive defeat associated with 20 August; the day-by-day narrative comes from much later sources.
Fred Donner cautions that the date of the Syriac fragment supporting 20 August cannot itself be established, so it may depend on the same later chronology as Islamic accounts.
Surviving Christian sources are terse, while detailed Arabic battle narratives were written substantially later. Command structure, maneuvers, troop composition, casualties, and even whether this was one battle or a linked Jabiya–Yarmouk campaign remain debated.
Army numbers vary enormously. Modern estimates do not support treating 25,000 Muslim troops—or a vast Byzantine numerical superiority—as certain.