1911 Encyclopædia Britannica/Ciudad Porfirio Diaz
CIUDAD PORFIRIO DIAZ, formerly Piedras Negras, a northern frontier town of Mexico in the state of Coahuila, 1008 m. N. by W. from Mexico City, on the Rio Grande del Norte, 720 ft. above sea-level, opposite the town of Eagle Pass, Texas. Pop. (1900, estimate) 5000. An international bridge connects the two towns, and the Mexican International railway has its northern terminus in Mexico at this point. The town has an important transfer trade with the United States, and is the centre of a fertile district devoted to agriculture and stock-raising. Coal is found in the vicinity. The Mexican government maintains a custom-house and military post here. The town was founded in 1849.