gradually evolved into the Ruthenian language. Polish rule, which came later, was accompanied by a more assimilationist policy. By the 1569 Union of Lublin that formed the Polish–Lithuanian Commonwealth, a significant part of Ukrainian territory was moved from Lithuanian rule to Polish administration, resulting in cultural Polonization and visible attempts to colonize Ukraine by the Polish nobility. Many Ukrainian nobles were forced to learn the Polish language and convert to Catholicism during that period in order to maintain their lofty aristocratic position. Lower classes were less affected because literacy was common only in the upper class and clergy. The latter were also under significant Polish pressure after the Union with the Catholic Church. Most of the educational system was gradually Polonized. In Ruthenia, the language of administrative documents gradually shifted towards Polish. The Polish language has had heavy influences on Ukrainian (particularly in Western Ukraine). The southwestern Ukrainian dialects are transitional to Polish. As the Ukrainian language developed further, some borrowings from Tatar and Turkish occurred. Ukrainian culture and language flourished in the sixteenth and first half of the 17th century, when Ukraine was part of the Polish–Lithuanian Commonwealth, albeit in spite of being part of the PLC, not as a result. Among many schools established in that time, the Kyiv-Mohyla Collegium (the predecessor of the modern Kyiv-Mohyla Academy), founded by the Moldavian Orthodox Metropolitan Peter Mogila, was the most important. At that time languages were associated more with religions: Catholics spoke Polish, and members of the Orthodox church spoke Ruthenian. After the Treaty of Pereyaslav, Ukrainian high culture went into a long period of steady decline. In the aftermath, the Kyiv-Mohyla Academy was taken over by the Russian Empire and closed down later in the 19th century. Most of the remaining Ukrainian schools also switched to Polish or Russian in the territories controlled by these respective countries, which was followed by a new wave of Polonization and Russification of the native nobility. Gradually the official language of Ukrainian provinces under Poland was changed to Polish, while the upper classes in the Russian part of Ukraine used Russian. During the 19th century, a revival of Ukrainian self-identification manifested in the literary classes of both Russian-Empire Dnieper Ukraine and Austrian Galicia. The Brotherhood of Sts Cyril and Methodius in Kyiv applied an old word for the Cossack motherland, Ukrajina, as a self-appellation for the nation of Ukrainians, and Ukrajins'ka mova for