By the 11th or 12th century, the rulers of kingdoms such as Takrur (a monarchy centred on the Senegal River just to the north), ancient Ghana and Gao had converted to Islam and had appointed to their courts Muslims who were literate in the Arabic language. At the beginning of the 14th century, most of what is today called the Gambia was part of the Mali Empire. The Portuguese reached this area by sea in the mid-15th century and began to dominate overseas trade.