The Spanish conquest of Petén was the last stage of the conquest of Guatemala, a prolonged conflict during the Spanish colonisation of the Americas. A wide lowland plain covered with dense rainforest, Petén contains a central drainage basin with a series of lakes and areas of savannah. It is crossed by several ranges of low karstic hills and rises to the south as it nears the Guatemalan Highlands. The conquest of Petén, a region now incorporated into the modern republic of Guatemala, climaxed in 1697 with the capture of Nojpetén, the island capital of the Itza kingdom, by Martín de Ursúa y Arizmendi. With the defeat of the Itza, the last independent and unconquered native kingdom in the Americas fell to European colonisers.
Sizeable Maya populations existed in Petén before the conquest, particularly around the central lakes and along the rivers. Petén was divided into different Maya polities engaged in a complex web of alliances and enmities. The most important groups around the central lakes were the Itza, the Yalain and the Kowoj. Other groups with territories in Petén included the Kejache, the Acala, the Lakandon Ch'ol, the Xocmo, the Chinamita, the Icaiche and the Manche Ch'ol.
Petén was first penetrated by Hernán Cortés with a sizeable expedition that crossed the territory from north to south in 1525. In the first half of the 16th century, Spain established neighbouring colonies in Yucatán to the north and Guatemala to the south. Spanish missionaries laid the groundwork for the extension of colonial administration in the extreme south of Petén from 1596 onwards, but no further Spanish entry of central Petén took place until 1618 and 1619 when missionaries arrived at the Itza capital, having travelled from the Spanish town of Mérida in Yucatán.
In 1622 a military expedition set out from Yucatán led by Captain Francisco de Mirones and accompanied by Franciscan friar Diego Delgado; this expedition was a disaster, and the Spanish were massacred by the Itza. In 1628 the Manche Ch'ol of the south were placed under the administration of the colonial governor of Verapaz within the Captaincy General of Guatemala. The Manche Ch'ol unsuccessfully rebelled against Spanish control in 1633. In 1695 a military expedition tried to reach Lake Petén Itzá from Guatemala; this was followed in 1696 by missionaries from Mérida and in 1697 by Martín de Ursúa's expedition from Yucatán that resulted in the final defeat of the independent kingdoms of central Petén and their incorporation into the Spanish Empire.
The modern department of Petén is located in northern Guatemala. It is bordered on the west by the Mexican state of Chiapas; this border largely follows the course of the Usumacinta River. On the north side Petén is bordered by the Mexican state of Campeche and on the northwest by the Mexican state of Tabasco; Petén is bordered on the east by Belize and on the south side by the Guatemalan departments of Alta Verapaz and Izabal.
The Petén lowlands are formed by a densely forested low-lying limestone plain featuring karstic topography. The area is crossed by low east–west oriented ridges of Cenozoic limestone and is characterised by a variety of forest and soil types; water sources include generally small rivers and low-lying seasonal swamps known as bajos. A chain of fourteen lakes runs across the central drainage basin of Petén; during the rainy season some of these lakes become interconnected. This drainage area measures approximately 100 kilometres (62 mi) east–west by 30 kilometres (19 mi) north–south. The largest lake is Lake Petén Itzá, near the centre of the drainage basin; it measures 32 by 5 kilometres (19.9 by 3.1 mi). A broad savannah extends south of the central lakes; it has an average altitude of 150 metres (490 ft) above mean sea level with karstic ridges reaching an average altitude of 300 metres (980 ft). The savannah features a compact red clay soil that is too poor to support heavy cultivation, which resulted in a relatively low level of pre-Columbian occupation. It is surrounded by hills with unusually steep southern slopes and gentler northern approaches; the hills are covered with dense tropical forest. To the north of the lakes region bajos become more frequent, interspersed with forest. In the far north of Petén the Mirador Basin forms another interior drainage region. To the south Petén reaches an altitude of approximately 500 metres (1,600 ft) as it rises towards the Guatemalan Highlands and meets Paleozoic metamorphic rocks.
The climate of Petén is divided into wet and dry seasons, with the rainy season lasting from June to December, although these seasons are not clearly defined in the south. The climate varies from tropical in the south to semitropical in the north; temperature varies between 12 and 40 °C (54 and 104 °F), although it does not usually drop beneath 18 °C (64 °F). Mean temperature varies from 24.3 °C (75.7 °F) in the southeast around Poptún to 26.9 °C (80.4 °F) around Uaxactún in the northeast. Highest temperatures are reached from April to June, and January is the coldest month; all Petén experiences a hot dry period in late August. Annual precipitation is high, varying from a mean of 1,198 millimetres (47.2 in) in the northeast to 2,007 millimetres (79.0 in) in central Petén around Flores (Nojpetén). The extreme southeast of Petén experiences the largest variations in temperature and rainfall, with precipitation reaching as much as 3,000 millimetres (120 in) in a year.