The Principality of Moscow or Grand Duchy of Moscow, also known simply as Muscovy, was a principality of the Late Middle Ages centered on Moscow. It eventually evolved into the Tsardom of Russia in the early modern period. The princes of Moscow were descendants of the first prince Daniel, referred to in modern historiography as the Daniilovichi, a branch of the Rurikids.
The seal of Simeon the Proud (1340s), reads: "The seal of the Grand Duke Simeon of all Rus'".
The Moscow Kremlin under Prince Ivan Kalita in the early 14th century, depicted by 19th century painter Apollinary Vasnetsov.
Dmitry Donskoi in the 1380 Battle of Kulikovo, painting by Adolphe Yvon, 1849
Andrei Rublev's famous icon of the Trinity
Russian is an East Slavic language, spoken primarily in Russia. It is the native language of the Russians and belongs to the Indo-European language family. It is one of four living East Slavic languages, and is also a part of the larger Balto-Slavic languages. It was the de facto and de jure official language of the former Soviet Union. Russian has remained an official language in independent Russia, Belarus, Kazakhstan, Kyrgyzstan, and Tajikistan, and is still commonly used as a lingua franca in Ukraine, Moldova, the Caucasus, Central Asia, and to a lesser extent in the Baltic states and Israel.
This page from an "ABC" book printed in Moscow in 1694 shows the letter П.
The Ostromir Gospels of 1056 is the second oldest East Slavic book known, one of many medieval illuminated manuscripts preserved in the Russian National Library.