The Alcázar of Segovia, like many fortifications in Spain, started off as an Arab fort, but little of that structure remains. The first reference to this particular Alcázar was in 1120, around 32 years after the city of Segovia returned to Christian hands (during the time when Alfonso VI of León and Castile reconquered lands to the south of the Duero river down to Toledo and beyond). However, archaeological evidence suggests that the site of this Alcázar was once used in Roman times as a fortification.
The shape and form of the Alcázar was not known until the reign of King Alfonso VIII (1155–1214), however early documentation mentioned a wooden stockade fence. It can be concluded that prior to Alfonso VIII's reign, it was no more than a wooden fort built over the old Roman foundations. Alfonso VIII and his wife, Eleanor of Plantagenet made this Alcázar their principal residence and much work was carried out to erect the beginnings of the stone fortification
The Alcázar, throughout the Middle Ages, remained one of the favorite residences of the monarchs of the Kingdom of Castile and a key fortress in the defense of the kingdom. It was during this period a majority of the current building was constructed and the palace was extended on a large scale by the monarchs of the Trastámara dynasty.
In 1258, parts of the Alcázar had to be rebuilt by King Alfonso X of Castile after a cave-in and soon after the Hall of Kings was built to house Parliament. However, the single largest contributor to the continuing construction of the Alcázar is King John II who built the 'New Tower' (John II tower as it is known today).