Yaxchilan flourished in the 8th and 9th centuries. The site contains extensive ruins, with palaces and temples bordering a large plaza upon a terrace above the Usumacinta River. The architectural remains extend across the higher terraces and the hills to the south of the river, overlooking both the river itself and the lowlands beyond. Yaxchilan is known for the large quantity of excellent sculpture at the site, such as the monolithic carved stelae and the narrative stone reliefs carved on lintels spanning the temple doorways. Over 120 inscriptions have been identified on the various monuments from the site. The major groups are the Central Acropolis, the West Acropolis and the South Acropolis. The South Acropolis occupies the highest part of the site. The site is aligned with relation to the Usumacinta River, at times causing unconventional orientation of the major structures, such as the two ballcourts. The site is relatively natural with howling monkeys, bats, toucans and other wildlife to be seen in and around the buildings.