Piedras Negras, city (1990 pop. 96,178), Coahuila state, N Mexico, on the Rio Grande opposite Eagle Pass, Tex. Founded in 1849, the city grew as an international shipping point. Piedras Negras is a commercial and processsing center for the surrounding agricultural region. Industry includes coal mining and metal-ore furnaces. In 1888, Piedras Negras was renamed Ciudad Porfirio Díaz in honor of the dictator, but the old name was restored after his overthrow.

Piedras Negras (pyā´ŧħräs nā´gräs) [Span.,=black stones], ruined city of the Classic era of the Maya, NW Petén, Guatemala, in the Usumacinta valley. Reaching a peak of sculptural achievement (according to one dating system, between 731 and 795), Piedras Negras developed some of the finest pre-Columbian stonework.