Chess is believed to have originated in northwest India, by about the early 7th century. Its early form was known as "chaturaṅga" (), literally "four divisions" the military – infantry, cavalry, elephants, and chariotry, represented by the pieces that would evolve into the modern pawn, knight, bishop, and rook, respectively. "Chaturanga" was played on an 8×8 uncheckered board, called "ashtāpada." Thence it spread eastward and westward along the Silk Road. The earliest evidence of chess is found in the nearby Sasanian Persia around 600, where the game came to be known by the name "chatrang". Chatrang was taken up by the Muslim world after the Islamic conquest of Persia (633–44), where it was then named "shatranj", with the pieces largely retaining their Persian names. In Spanish "shatranj" was rendered as "ajedrez" ("al-shatranj"), in Portuguese as "xadrez", and in Greek as ζατρίκιον ("zatrikion", which comes directly from the Persian "chatrang"), but in the rest of Europe it was replaced by versions of the Persian "shāh" ("king"), which was familiar as an exclamation and became the English words "check" and "chess". The word "checkmate" is derived from the Persian "shāh māt" ("the king is helpless").