St. Leonard's Crypt under the Wawel Castle in Kraków, Poland, is a Romanesque crypt founded in the 11th century (around 1038 – 1039) by Casimir I the Restorer who made Kraków his royal residence as the capital.
At the end of the 11th century construction work began on the cathedral called ‘Hermanowska’. It is probable that Władysław I Herman was its benefactor. The cathedral was consecrated in 1142. More is known about this new structure because its image is featured on a chapterhouse seal from the 13th century and its present day remnants are well preserved – including the lower part of the Silver Bell Tower.
The entire St. Leonard's Crypt under the ‘Hermanowska’ cathedral, with its trinaval, is supported by eight columns. In 1118 bishop Maurus was buried there. The paten and the chalice were later exhumed from the tomb. This period also gave rise to the Rotunda by the Bastion of Ladislaus IV of Hungary from the 12th century, which could have been a baptistery for the royalty, the Church near the Dragon’s Den, and the Rotunda by the Sandomierska Tower – probably from the second half of the 11th century.
The crypt holds the tombs of Polish kings and heroes such as: Michał Korybut Wiśniowiecki - King of the Polish-Lithuanian Commonwealth, Jan III Sobieski - also King of the Polish-Lithuanian Commonwealth and Commander of the Holy League at the Battle of Vienna, Maria Kazimiera - Queen of the Polish-Lithuanian Commonwealth and consort to Jan III Sobieski, Józef Poniatowski - Prince of Poland and Marshall of France, Tadeusz Kościuszko - Polish general, revolutionary and a Brigadier General in the American Revolutionary War, Adam Mickiewicz (laid to rest there in 1890) and Juliusz Slowacki (1927), as well as Władysław Sikorski - Prime Minister of the Polish Government in Exile and Commander-in-Chief of the Polish Armed Forces