| Conflict: | Battle of St. Matthew's Day |
| Partof: | Northern Crusades |
| Date: | 21 September 1217 |
| Place: | Near Viljandi, Estonia. |
| Result: | Livonian victory |
| Combatant1: | Counties of Ancient Estonia |
| Combatant2: | Sword Brethren Livonians Latgalians |
| Commander1: | Lembitu of Lehola Vootele Manivald Unnepeve |
| Commander2: | Volquin Caupo of Turaida Bernard II of Lippe |
| Strength1: | 6,000 |
| Strength2: | 3,000 |
| Casualties1: | ~1,000 (Henry of Latvia) |
| Casualties2: | ~100 |
The Battle of Matthew's Day (et|Madisepäeva lahing) was fought near Viljandi (probably in Vanamõisa) on 21 September 1217[1] [2] during the Livonian Crusade. The adversaries were the Sword Brethren (a German Crusading order) with their recently converted Livonian and Latgalian allies versus an army of 6,000 Estonian men from different counties, led by Lembitu, who had attempted to unify the Estonians. The Germans won, although the converted Livonian chieftain Caupo of Turaida died. Lembitu was also killed, and many other Estonians were forced to convert.