On September 22, Latvia and Lithuania celebrate the Day of the Baltic Unity. This holiday was established in 2000 to commemorate the Battle of Saule which was fought in 1236. In this battle, Baltic tribes defeated the Livonian Brothers of the Sword.

The Battle of Saule took place during the Livonian Crusade. The Livonian Brothers of the Sword intended to conquer pagan Baltic tribes and convert them to Christianity. On September 22, 1236, the knights invaded the region of Samogitia and met with resistance from the local tribes led by Vykintas, the Duke of Samogitia. The battle resulted in a decisive Samogitian victory. This victory inspired the tribes that had already been conquered to rebel against the Sword-Brothers.

In 2000, the parliaments of Latvia and Lithuania decided to commemorate the battle by declaring September 22 to be celebrated as the Day of Baltic Unity. The holiday has been observed annually ever since. It is designed to bring the Baltic peoples together and foster strong ties between the two Baltic states. The Day of Baltic Unity is marked with official receptions, conferences, exhibitions, cultural events, concerts and other appropriate events and activities.