El Cayo was a major Maya city from the Usumacinta region subordinated for a period to Piedras Negras.

The Altar illustrates the image of Aj Chak Wayab' K'utim sitting in front of a censer performing an end-of-cycle ceremony on the long count date of 9.15.0.0.0 4 Ajaw 13 Yax, which corresponds to August 18, 731 AD.

Then it narrates that on April 18, 763, a ruler of Piedras Negras participated in the ceremony of ascension to power of Chan Panak' Wayib for his future succession to the tilte of sajal.

[4] The site was discovered and first documented in 1897 by Teobert Maler during an expedition on the Usumacinta region where he recorded the presence of several monuments and a ruined main palace.

In 1997, a group of archaeologists including Peter Mathews, tried to extract Altar 4 to take it to a museum but they were attacked and kidnapped by local indigenous people accusing them of being looters, after some days they were found in the middle of the jungle, this incident ended every archaeological research and cancelled any further investigations in the site until today.