In 1345, thieves broke into the parish church of All Saints in Kraków and stole the silver ciborium together with the consecrated hosts. Realising the hosts were not negotiable, they cast them into the marsh outside the city. Days later villagers reported a bright light over the marsh; investigation found the hosts intact, suspended just above the water.
King Casimir the Great vowed to build a great church on the spot. The Corpus Christi Basilica (Bazylika Bożego Ciała), built 1340–1405 and still standing in the Kazimierz district of Kraków, is the result. The relic was preserved within. The basilica was a favourite of St. John of Kęty and a key formation site for the early Polish Catholic clergy.