ThePetén Basin is a geographical subregion of theMaya Lowlands, primarily located in northernGuatemala within theDepartment of El Petén, and into the state ofCampeche in southeasternMexico.
During the Late Preclassic and Classic periods ofpre-ColumbianMesoamerican chronology many major centers of theMaya civilization flourished, such asTikal andCalakmul.[1] A distinctive Petén-style ofMaya architecture andinscriptions arose. The archaeological sitesLa Sufricaya andHolmul are also located in this region.
By the first half of the 1st millennium BCE, the Petén andMirador Basin of this region were already well-established with a number ofmonumental sites and cities of theMaya civilization. Significant Maya sites of this Preclassic era ofMesoamerican chronology includeNakbé,El Mirador,Naachtun,San Bartolo andCival in theMirador Basin.[citation needed]

Later, Petén became the heartland of the Maya Classic Period (c. 200 – 900 CE). At its height around 750 it is estimated that the Petén Basin was home to several million people, being one of the mostdensely populated regions of the world at the time. Some areas are estimated to have had ca 2,000 people/km2.Mesoamerican agriculture was very extensive, and there is some evidence suggesting that the land was depleted by unsustainableoverfarming, resulting in afamine which was an important factor in the collapse of theClassic Maya states of this area. The population is estimated to have dropped by two-thirds between the mid 9th century and the mid 10th century.
Archaeological sites preserve important remnants of the Classic Maya in Petén Basin, such as:

Tikal National Park is one of the only sites to be designated aWorld Heritage Site for both archaeological and biodiversity reasons.[2] Many thousands of house mounds where worshipers and workers once lived were discovered at Tikal.[3]
After the Classic Period collapse the population of the area continued to drop dramatically, especially after the introduction ofsmallpox along with European explorers. The smallpox plague arrived around 1519 or 1520, preceding by several years the firstEuropeans to visit the region.Hernán Cortés led the first expedition to pass through the Petén Basin, in 1524 to 1525, and reported that the region mostly had small hamlets separated by thick forest, withTayasal being the only sizable inhabited city they observed.
After Cortés' expedition, thecolonial Spanish largely tried toconquer Petén Basin, with several attempts mainly fromBelize andAlta Verapaz, for generations until an expedition fromYucatán,Belize andCobán inAlta Verapaz, succeeded in conquering the last independent Mayapolities around 1697, such asZacpeten (capital of theKowoj Maya), theItza Maya center ofTayasal, and other towns in the Lake Petén Itza region such as Quexil (modern Spanish name, in Maya:Ek'ixil) andYalain. (see:Spanish conquest of Yucatán).
The Spanish town of Flores was established atop the site ofTayasal, but this remained an isolated backwater through the colonialViceroyalty of New Spain era and after Mexican independence. When Guatemalan PresidentRafael Carrera sent a small force to Flores to claim the region for Guatemala in the 1840s, the governments ofMexico and the state ofYucatán decided the Petén Basin area was not worth the trouble of contesting.