Receiving a charter from King Manuel I in 1512, Entradas was the seat of the municipality until 1836, when it was part of the municipality of Castro Verde. Historically, this territory has played an important strategic role. Not only because the old road that connected the river port of Mértola to the interior of Baixo Alentejo passes through here, but also because it is located at the "entrance" to Campo Branco, a destination for large flocks of sheep belonging to the Royal Household, especially in the 15th to 17th centuries.

Castro Verde is located in Baixo Alentejo, in the Alentejo region, in an area known as Campo Branco. A large part of the municipality's territory is within an area of ​​the European Union's Natura 2000 Network, represented by a Special Protection Area for endangered steppe bird species, such as the great bustard and the lesser kestrel. The municipality’s borders are marked on the roadsides leading to the territory’s limits with the municipality’s logotype emblem – the municipality’s landmark – “A window over the plain”.

The prehistory of the Baixo Alentejo region dates back to 200,000 BC, a period in which the territory is known to have been the habitat of Neanderthals migrating from northern Europe during the Lower Paleolithic period. These cultures continued to exist until around 28,000 BC when Neanderthal man faced extinction, with his last refuge being what is now Portugal.

This southwestern area of ​​Iberia was a region inhabited by various cultures. This was due to its strategic trading position on the Mediterranean, with the presence of abundant mineral wealth. Settlement began with the migration of the Celtiberians to Central Iberia in the 6th century BC, followed by the settlement of the Celts in the Alentejo region. From the 3rd century BC onwards, the basic Celtiberian settlements were replaced by the opido, a fortified and organized settlement with a defined territory that included the castros (Castro culture) as subordinate subdivisions.