This is a Royal Copenhagen commemorative plate. It depicts the Battle Lyndanisse on 05/06/1219.
The Battle of Lyndanisse was a battle during the Livonian Crusade, fought between the Kingdom of Denmark with various German allies and pagan Estonian tribes. The battle helped King Valdemar II of Denmark establish the territory of Danish Estonia during the Northern Crusades, which were undertaken in response to calls from the Pope. The Danes defeated the Estonians. Today, the Battle of Lyndanisse is perhaps best known for a legend that the Danish flag, the Dannebrog, fell from the sky just as the Danes were about to lose the battle.
The plate is 20.50cm in diameter.