Gąsawa massacre: At an assembly of Piast dukes at Gąsawa, Polish Prince Leszek the White, Duke Henry the Bearded and others are attacked by assassins while bathing.

The Gąsawa massacre was an attack on the night of 23-24 November 1227, during a council of Polish Piast dukes that was being held near the village of Gąsawa in Kuyavia, Poland. The High Duke of Poland, Leszek the White, was assassinated, and Duke Henry the Bearded of Silesia was gravely wounded.