King Mindaugas, the man who unified the Lithuanian tribes in the 13th century, converted to Christianity in 1251 - a strategic baptism that earned him a papally-sanctioned crown - and is believed to have ordered the first cathedral built on the site. After his murder in 1263, Lithuania snapped back to its older gods, and the cathedral once again served as a place of pagan worship. Lithuania remained the last pagan state in Europe until 1387, when Grand Duke Jogaila accepted Christianity as part of the deal that made him King of Poland. Construction began that year on a Gothic cathedral with five chapels. It burned down in 1419. Vytautas the Great rebuilt it as a larger Gothic church in preparation for his 1429 coronation as King of Lithuania - a coronation that never happened because the crown sent from Rome was intercepted by Polish nobles who did not want a separate Lithuanian kingdom. Vytautas's walls and pillars are still inside the building.

The cathedral's crypts and catacombs hold a roster of who decided what in this part of Europe for four centuries. Vytautas himself (died 1430), his wife Anna (1418), his brother Sigismund Kęstutaitis (1440), his cousin Švitrigaila (1452), Saint Casimir (1484), Alexander Jagiellon (1506), and two of Sigismund II Augustus's wives - Elisabeth of Austria (1545) and Barbara Radziwiłł (1551), the great love of his life whose death he never recovered from. The heart of King Władysław IV Vasa rests here, though his body lies at Wawel in Kraków. From 1529 until 1569, when the Union of Lublin merged Poland and Lithuania, Lithuanian Grand Dukes were invested in this cathedral with Gediminas's Cap, a ceremony separate from coronation as King of Poland. On 29 May 1580, even after the Union, Bishop Merkelis Giedraitis presented Stephen Báthory with a sword and pearl-studded hat blessed by Pope Gregory XIII himself - a ceremony that quietly insisted Lithuania was still its own thing.

Between 1623 and 1636, Sigismund III Vasa commissioned what would become the cathedral's masterpiece: the Baroque Chapel of Saint Casimir, designed by royal architect Costante Tencalla and built of Swedish sandstone. His son Władysław IV Vasa finished it. Reconstructed in 1691-1692, it received frescoes by Michelangelo Palloni and altar work by Pietro Perti. The chapel holds sculpted statues of the Jagiellon kings and an epitaph containing Władysław IV's heart. Its silver-and-gilt theatricality contrasts with the austere Neoclassical cathedral around it - a small Italian baroque jewel set inside what reads, externally, as a Greek temple. More than any single space here, this chapel symbolized the Polish-Lithuanian union: a chapel built by Polish-Vasa kings to honor a Lithuanian-Polish saint, decorated by Italians, in a cathedral founded on a Baltic pagan site.

In 1769 the southern tower, rebuilt after a 1666 fire, suddenly collapsed - destroying the vaults of a neighboring chapel and killing six people. Bishop Ignacy Jakub Massalski commissioned a complete reconstruction, and architect Laurynas Gucevičius - a student of Claude Nicolas Ledoux - reshaped the cathedral into the strict Neoclassical quadrangle visible today. Italian sculptor Tommaso Righi added the four evangelists across the main facade. Between 1786 and 1792, three sculptures by Kazimierz Jelski went up on the roof: Saint Casimir for Lithuania on the south, Saint Stanislaus for Poland on the north, and Saint Helena holding a 9-meter golden cross in the center. Soviet authorities removed them in 1950 and converted the cathedral into a warehouse. The sculptures were restored in 1997, the cathedral itself returned to worship in 1988-89, and a thorough renovation in 2006-2008 finally repaired what generations of damp and neglect had done.

When restoration work descended into the foundations in the late 20th century, archaeologists pulled the cathedral's biography out of the dirt: the altars of the presumed pagan temple, the original floor laid in Mindaugas's time, walls from the 1387 Gothic cathedral, and the 14th-century fresco - oldest in Lithuania, found on the wall of an underground chapel. Above ground, the bell tower stands separate from the cathedral, set back across the square; it sits atop a defensive tower of the old Lower Castle. Behind the cathedral, work began in 2002 to reconstruct the Royal Palace of Lithuania, which had been demolished in the 19th century. The new palace changed the cathedral's setting fundamentally. Look across Cathedral Square today and the layers stack: pagan temple, Mindaugas's cathedral, Vytautas's Gothic walls, Tencalla's Baroque chapel, Gucevičius's Neoclassical facade, the bell tower, the rebuilt palace, and underfoot, that one tile that recalls how two million people once stood on this exact ground and ended an empire.