The term Mindanao [2] or Magindanao was originally given to the town now known as Cotabato and its immediate vicinity. As the power of the sultan of Magindanao extended over the adjacent territory it was next applied to the lower Rio Grande Valley and later to all the valley and the whole seacoast that was brought under the rule of the sultan. The word is derived from the root "danao," which means inundation by a river, lake, or sea. The derivative "Mindanao" means "inundated" or "that which is inundated." "Magindanao" means "that which has inundation." This is the most appropriate term which could have been given to this land. For more than 10 miles from the sea the Rio Grande, aided by the rise of the tide, periodically overflows its banks and floods all the adjacent lands. In the rainy season this inundation extends farther up and includes an extensive tract of country. The word "Cotabato" is in Moro kuta watu, which means a stone fort. Batu is the equivalent of watu in Malay, Sulu, Tagalog, and Visaya. This name is very modern, for the older maps that are still in use give the name Mindanao in place of Cotabato. The little stream that rises in the sulphur springs of Cotabato and empties into the Rio Grande at its junction with the Matampay in front of the present guardhouse is still known as the Stream of Magindanao. The name of the Rio Grande in the Magindanao dialect is "Pulangi," which means "large river." The Rio Grande divides, 20 miles before it reaches the sea, into the north branch and the south branch. Cotabato is situated on the left bank of the north branch, about 5 miles from its mouth. The hill of Cotabato is called "Tantawan," which means "extensive view." Paygwan means "the place of washing," and is on the left bank of the river at its mouth and above the bar. The Spanish maps give it as Paiuan. Tinundan is at the mouth of a dead estuary of the same name that joins the Pulangi about half a mile above Paygwan and on the same side. Slangan is the western part of present Cotabato and extends along the Manday stream. The Moros call the Manday "Masurut." Simway extends along the river of the same name for about 2 miles from its mouth and lies about 4 miles north of Cotabato.