Away, on the left bank of the Usumacinta river, stand the ruins of Men-che or Lorillard city.
It is an arbitrary line and follows only two natural lines of demarcation - the Suchiate river from the Pacific coast to its source, and the Chixoy and Usumacinta rivers from near the 16th parallel N.W.
Between these rivers the boundary line is determined by the peaks of Tacana, Buenavista and Ixbul, and from the Usumacinta eastward it follows two parallels of latitude, one on the point of departure from that river, and the other, the longer, on that of 1 7° 49' to the British Honduras frontier.
The largest rivers of Mexico are: the Rio Grande de Santiago, called the Lerma above Lake Chapala, rising in the state of Mexico and flowing westward across Guanajuato, Jalisco and Tepic to the Pacific coast, with a total length of 540 m., celebrated for its deep canyons and waterfalls; the Rio de las Balsas, or Mescala, which rises in Tlaxcala and flows south and west to the Pacific with a course of 426 m.; the Yaqui, which rises in western Chihuahua and, after breaking through the northern ranges of the Sierra Madre Occidental, flows south-westerly across Sonora to the Gulf of California, with a length of 390 m.; the Grijalva, also called the Chiapas on its upper course, which has its sources in the state of Chiapas and flows north-west and north across Tabasco to the Gulf of Mexico, with a total length of 350 m.; the Fuerte, which rises in southern Chihuahua and, after breaking through the sierras, flows south-west across Sinaloa to the Gulf of California, with a course of 340 m.; the Usumacinta, which is formed by the confluence of the Chixoy and Pasion on the east frontier of Chiapas, and flows north-west across Tabasco to the Grijalva, with a course of 330 m.; and the Panuco, which has its source in the north-west of the state of Mexico and flows north-eastward to the Gulf of Mexico.
The more important of these are in Tabasco - the Grijalva, navigable for about 93 m., and the Usumacinta, for about 270 m.
A vast number of streams, among which are the Chixoy, the Guadalupe, and the Rio de la Pasion, unite to form the Usumacinta, whose noble current passes along the Mexican frontier, and flowing on through Chiapas and Tabasco, falls into the Bay of Campeche.
Two large rivers, the Grijalva and Usumacinta, traverse its territory.
The Usumacinta likewise has its sources in western Guatemala.
The Usumacinta, including its head streams, is about 500 m.