The earliest inhabitants of Altar de Sacrificios may not have been Maya at all. Archaeological evidence suggests the site was first settled around 800 BCE, at the beginning of the Middle Preclassic period, possibly by Mixe-Zoquean people who arrived from the west. These first residents lived at ground level in houses built from perishable materials - wood, thatch, palm - leaving little behind except the traces of their presence in the soil. They had not yet developed the extensive trade networks that would later define the region's economy. Between 600 and 300 BCE, the settlement began to take on the character of a ceremonial center, with houses built on terraces for the first time. At some point during the later Preclassic, Maya peoples settled the site. The transition from one culture to another is recorded not in any written inscription but in the changing styles of pottery and architecture that archaeologists have painstakingly cataloged across the island's stratified layers.

By the seventh century CE, Altar de Sacrificios had reached its height. New and existing buildings were faced with limestone, and a ballcourt was constructed to separate the North and South Plazas of Group A. Monuments multiplied. Fine goods appeared in burials: pyrite mirrors that caught the jungle light, flint projectile points, and beads carved from jadeite. Stela 10, bearing the earliest legible date at the site - August 28, 455 CE - was erected at Group B, the location of the main pyramid, which measures 36 meters at its base and stands 13 meters tall. The site's 29 inscribed monuments span nearly four centuries, from 455 to 849 CE, though most are so badly eroded as to be unreadable. Among the more revealing discoveries is Burial 128, an elite tomb built into Structure A-III: stone-lined with a wooden ceiling, it contained the remains of a woman in her forties placed on a straw mat, surrounded by ceramics, jade, pyrite, bone, and shell.

The most intriguing chapter at Altar de Sacrificios is its final one. By the eighth and ninth centuries, as the Classic Maya world entered its long collapse, the population was falling and construction quality declining. Then, around 900 to 950 CE, something unexpected happened. Fine paste ceramics appeared depicting people with distinctly different features from earlier styles. The evidence suggests that foreigners - likely Chontal Maya traders who dominated the Usumacinta's riverine commerce - moved into the site during its twilight. Nearby Seibal experienced a similar resurgence at the same time, both cases linked to the disintegration of the Petexbatun kingdom based at Dos Pilas. For a brief period, the newcomers brought fresh energy to a dying settlement. But the trade routes that had sustained the Usumacinta corridor were themselves collapsing as the great upstream cities fell silent. River commerce declined drastically, and the outsiders could not revive what the broader region could no longer support.

The final residents of Altar de Sacrificios withdrew into defensible positions on the island, a community turning inward as the world it had known for over a millennium dissolved around it. There is little evidence of any occupation after roughly 950 CE. The jungle reclaimed the plazas and pyramids. Teobert Maler found the ruins in 1895 and gave them their evocative, inaccurate name. Sylvanus Morley described the hieroglyphic inscriptions in his 1938 work The Inscriptions of Peten. But the most comprehensive investigation came between 1958 and 1963, when archaeologists A. Ledyard Smith and Gordon Willey of Harvard's Peabody Museum spent five seasons excavating the island. Their work revealed the full arc of occupation: from pre-Maya settlers through the Classic Maya golden age to the strange, brief revival by foreign traders and the final abandonment. The confluence of the two rivers still flows past the island, as it did when the first Mixe-Zoquean families built their perishable houses on its banks nearly three thousand years ago.