Catherine marries the heir to the Russian throne, Grand Duke Peter, in St Petersburg on 21 August 1745.
On 21 August 1745, sixteen-year-old Catherine married Grand Duke Peter of Holstein-Gottorp, heir to the Russian imperial throne, in a lavish ceremony in St Petersburg orchestrated by Empress Elizabeth. The wedding was celebrated with extraordinary pomp, including days of festivities, fireworks, and banquets befitting the union of the future rulers of the Russian Empire.
The marriage, however, proved deeply unhappy from its earliest days. Peter was immature, often cruel, and reportedly more interested in playing with toy soldiers than in his young bride; the couple's relationship remained unconsummated for years, causing considerable anxiety at court over the succession. Catherine, isolated and unloved, turned to voracious reading of Enlightenment philosophy, French literature, and political theory, cultivating the formidable intellect that would later define her reign.
Despite its personal unhappiness, the marriage was politically essential: it formally tied Catherine to the Romanov line and positioned her as the future empress consort. The union produced her son and heir, Paul, in 1754, though his paternity was long rumored to lie elsewhere. Ultimately, Catherine's unhappy marriage became the crucible in which her political ambition and self-reliance were forged, culminating in her 1762 coup against Peter after he ascended briefly as Emperor Peter III.