And in fact, Moscow became the seat of the Eastern Orthodox Church in 1325, when the metropolitan Peter moved there. So you might think that the Muscovites would be grateful for all of this help from the Mongols. But you would be wrong. In fact, as the Mongols' position weakened in Russia in the latter half of the 14th century, one of Moscow's princes, Dmitry Donskoy, made war on them and inflicted the first major defeat of Mongols in Russia at the Battle of Kulikovo Field. This showed that the Mongols weren't invincible, which is always really bad for an imperial force. Plus, it made Moscow look like the hero of the Russians. And that helped strengthen the idea of a unified Russia, just as you'll remember the Persians helped unify the Greeks a long time ago.