I think you mean Moscow. Very simply, the first Rome is Rome, the seat of the Christian church, which was invaded by Barbarians at the fall of the Roman Empire.

The second "Rome" was Constantinople (now called Istanbul) which was the capital of Byzantium, or the Eastern Roman Empire. This was Christian, and the historical seat of Orthodoxy, which split with the Roman Catholic Church in 1054.

Constantinople, and along with it the Byzantine Empire, survived until 1453, when it was overrun by the Muslim Ottomans.

So now, with Rome no longer being the home of the true church, (according to the Orthodox), and with the home of Orthodoxy overrun by Muslim invaders, what's left? Moscow, at this time, the capital of Russia, an Orthodox nation.

This may seem like ancient history, or just an abstraction. But this belief, which is endorsed by the powerful Russian Orthodox Church today, is still seen as a big deal. The Russian church doesn't think much of the current Constantinople-based church (it is now very small), and they have by far the largest number of followers.

This is evidenced by the fact that the recent Orthodox synod (is it called that?) was boycotted by the Russian church, effectively neutering it.