The Arch Cathedral of St John is one of the oldest in the Polish capital. The historic church was almost completely destroyed during World War II.

It has since been painstakingly restored, retaining its noble gothic facade, though having lost its opulent, baroque interior. With a lofty, vaulted ceiling and some striking stained glass windows, the interior is now more gothic in character. Its crypt, which is the last resting place of generations of bishops, dukes, and other eminent Poles, has survived the ravages of time largely unscathed.

The remains of the Dukes of Masovia, King Stanisław August Poniatowski, and statesman Stanisław Małachowski are interred inside. Poniatowski was the King of Poland and Grand Duke of Lithuania, the last ruling monarch of the commonwealth. Malachowski was the first Prime Minister of Poland.

Born into an influential family on a large estate in present-day Belarus, Poniatowski was well-read, as well as a connoisseur of the arts and a reformer. He introduced the Constitution of Poland in 1791, the first codified constitution in Europe. Unfortunately, Poniatowski had powerful enemies and few friends. 

Forced to abdicate his throne following the final partition of Poland, he lived his last years on a meager pension in St. Petersburg as a ward of the Russian Tsar. During the Soviet regime, his body was exhumed from the church where he was buried and shipped to his birthplace. He was interred, for the second time, in the crypt of his family chapel in the village of Volchyn in Belarus. In 1995, his remains were moved one last time, to his final resting place in the Arch Cathedral of St Johns in Warsaw, almost 200 years after his death.