Several archaeological findings show that in prehistoric times these lands were already inhabited. In the Atapuerca Mountains have been found many bones of the ancestors of Homo sapiens, making these findings one of the most important to determine the history of human evolution. The most important discovery that catapulted the site to international fame was the remains of Homo heidelbergensis.

Before the arrival of the Romans, it is known that the territories that make up Castile and León today were occupied by various Celtic peoples, such as Vaccaei, Autrigones, Turmodigi, the Vettones, Astures or Celtiberians. The Roman conquest resulted in warring with the local tribes. One particularly famous episode was the siege of Numantia, an old town located near the current city of Soria.

The romanization was unstoppable, and to this day great Roman works of art have remained, mainly the Aqueduct of Segovia as well as many archaeological remains such as those of the ancient Clunia, Salt mines of Poza de la Sal and the vía de la Plata pathway, which crosses the west of the community from Astorga (Asturica Augusta) to the capital of modern Extremadura, Mérida (Emerita Augusta).

With the fall of Rome, the lands were occupied militarily by the Visigoth peoples of Germanic origin. The subsequent arrival of the Arabs was followed by a process known as the Reconquista. In the mountainous area of Asturias, a small Christian kingdom was created which opposed the Islamic presence in the Peninsula. They proclaimed themselves heirs of the last Visigoth kings, who in turn had been deeply romanized. This resistance of Visigoth-Roman heritage and supported by Christianity, was becoming increasingly strong and expanding to the south, eventually setting its court in the city of León, becoming the Kingdom of León. To favor the repopulation of the new reconquered lands, a number of fueros or letters of repopulation were granted by the monarchs.

In the Middle Ages the pilgrimage by Christianity to Santiago de Compostela was popularized. The Camino de Santiago runs along the northern part of the region, and contributed to the spread of European cultural innovations throughout the peninsula. Today the Camino is still an important touristic and cultural attraction.

In 1188, the basilica of San Isidoro of León was the setting of the first parliamentary body in the history of Europe, with the participation of the Third Estate. The king who summoned it was Alfonso IX of León.

The legal basis for the kingdom was the Roman law, and because of this the kings increasingly wanted more power, like the Roman emperors. This is very clearly seen in the Siete Partidas of Alfonso X of Castile, which shows the imperial monism that the king sought. The King did not want to be a primus inter pares, but the source of the law.

Simultaneously, a county of this Christian kingdom of León, began to acquire autonomy and to expand. This is the primitive County of Castile, which would grow into a powerful kingdom among the Christian kingdoms of the Peninsula. The first Castilian count was Fernán González.

León and Castile continued to expand to the South, even beyond the Douro river, seeking to conquest lands under Islamic rule. That was the time of the Cantares de gesta, poems which recount the great deeds of the Christian nobles who fought against the Muslim enemy. Despite this, Christian and Muslim kings maintained diplomatic relations. One clear example is Rodrigo Díaz de Vivar, El Cid, paradigm of the medieval Christian knight, who fought both for Christian and Muslim kings.

The origin of the definitive dynastic unification of the kingdoms of Castile and León, which had been separated for just seven decades, was in 1194. Alfonso VIII of Castile and Alfonso IX of León signed in Tordehumos the treaty that pacified the area of Tierra de Campos and laid the foundation for a future reunification of the kingdoms, consolidated in 1230 with Ferdinand III the Saint. This agreement is called the Treaty of Tordehumos.

Pantheon of kings of the Romanesque Basilica of San Isidoro of León where Alfonso IX convened the Cortes of León of 1188, the first parliamentary body of the history of Europe, with presence of Third Estate. In the same basilica is the Chalice of Doña Urraca, which some researchers assimilate with the Holy Grail.

During the Late Middle Ages there was an economic and political crisis produced by a series of bad harvests and by disputes between nobles and the Crown for power, as well as between different contenders for the throne. In the Cortes of Valladolid of 1295, Ferdinand IV is recognized as king. The painting María de Molina presents her son Fernando IV in the Cortes of Valladolid of 1295 presides today the Spanish Congress of Deputies along with a painting of the Cortes of Cádiz, emphasizing the parliamentarian importance that has all the development of Cortes in Castile and León, despite its subsequent decline. The Crown was becoming more authoritarian and the nobility more dependent on it.

The reconquista continued advancing in this thriving Crown of Castile, and culminated with the surrender of the Nasrid Kingdom of Granada, last Muslim stronghold in the Peninsula, in 1492.