Latin, the learned lingua franca of Western Europe, was lingua non grata in Muscovy, where Slavonic reigned as the idiom of liturgy and literacy. Foreign visitors often belittled Russians for their ignorance of classical tongues. Yet, starting at the time of Peter the Great's cultural revolution, Russian elites increasingly turned to Latin as a vital semiotic resource. Taking an imaginary tour of Petropolis, as St. Petersburg was sometimes called, this article charts where and how the language was used, from the fledgling Academy of Sciences to the spectacles of imperial propaganda, with textual examples along the way. It shows that the take-up of Latin was an uneven and contested affair. Given the Russian church's tradition of anti-Catholic rhetoric, the most surprising development was the pride of place given to Latin in Orthodox seminary education. The most consequential was arguably Peter's promotion of a Latinate “civil” script. Much as the architecture in his new capital diverged from the picturesque structures of old Moscow, this streamlined writing system marked a significant departure from the hieratic letterforms of Slavonic. The new script – essentially the Cyrillic alphabet used to this day – is a lasting symbol of Russia's Latin interregnum, hiding in plain sight.