Polish began to emerge as a distinct language around the 10th century, the process largely triggered by the establishment and development of the Polish state. Mieszko I, ruler of the Polans tribe from the Greater Poland region, united a few culturally and linguistically related tribes from the basins of the Vistula and Oder before eventually accepting baptism in 966. With Christianity, Poland also adopted the Latin alphabet, which made it possible to write down Polish, until then existing only as a spoken language. "It is worth mentioning," writes Tomasz Kamusella, "that Polish is the oldest, non-ecclesiastical, written Slavic language with a continuous tradition of literacy and official use, which has lasted unbroken from the 16th century to this day."
The precursor to modern Polish is the Old Polish language. Ultimately, Polish is thought to descend from the unattested Proto-Slavic language. Polish was a lingua franca from 1500–1700 in Central and small portions of Eastern Europe, because of the political, cultural, scientific and military influence of the former Polish–Lithuanian Commonwealth.
"Day, ut ia pobrusa, a ti poziwai", highlited in red
The Book of Henryków (Polish: Księga henrykowska, Latin: Liber fundationis claustri Sancte Marie Virginis in Heinrichau), contains the earliest known sentence written in the Polish language: Day, ut ia pobrusa, a ti poziwai (pronounced originally as: Daj, uć ja pobrusza, a ti pocziwaj, modern Polish: Daj, niech ja pomielę, a ty odpoczywaj or Pozwól, że ja będę mełł, a ty odpocznij, English: Come, let me grind, and you take a rest), written around 1270.
The medieval recorder of this phrase, the Cistercian monk Peter of the Henryków monastery, noted that "Hoc est in polonico" ("This is in Polish").