In the middle there is a grave of bishop Maur, who died in 1118, discovered in 1938 during archaeological examination. The crypts also entomb other personae who are regarded as national heroes: King John III Sobieski, Queen Marie Casimire, Prince Józef Poniatowski and Marshal Władysław Sikorski. The vault also features a magnificent sarcophagus of Tadeusz Kościuszko. In 1977 a bronze commemorative plaque was placed next to it, as a gift from the American Congress on the 200th anniversary of the battle of Saratoga.