The fortress of Ilia has been historically mentioned in written documents starting with the middle of the 15th century. Its owners in the 16th century were all descendants of the Dienesi family, a well-known landlord family in the medieval county of Hunedoara
After the Ottomans conquered the fortress of Lipova in 1552, Ilia became a border citadel. To meet the requirements of its new position, the settlement was fortified with a defensive wall ring and towers. Later, as the original owner family died out without descendants, the domain was given by Prince Ștefan Báthory (1571–1586) to Farkas Bethlen of Iktár (1530–1590). He was the one that built the Red Bastion in 1582 and closed together the old fortified ring. This bastion, smaller in size and less exposed to attack, was designed as a dwelling tower from the very beginning, decorated with stone sculptural works and exterior paintings. According to the 1640-1713 inventaires of the domain, the fortified ring had a medieval dwelling tower and a manor built around 1629. The dwelling tower was the owners’ residence and in this tower in 1580, Gabriel Bethlen, the son of Farkas Bethlen and the future Prince of Transylvania between 1613–1629, was born.
The birthplace was marked with a commemorative stone, made in Cluj in 1627, which included the coat of arms and an inscription. The manor, a more comfortable dwelling, was built by Stephan, the younger brother of the prince. In 1670, it was decided that the other three bastion towers together with the fortified walls be demolished, so that Ilia could not serve as a military base for the Ottomans already camped at Lipova. At that time the domain had already passed to the grandchildren of the family Thököly of Stephan Bethlen.
Around 1678 the manor was extended by Emeric Thököly the future prince of Transylvania. The domain was bought in 1716 by Ioan Kászoni, the vicechancelor of Transylvania, the founding father of the baronial family of Bornemisza de Kászon. His descendants demolished the dwelling tower and the manor. Instead the baron Ignație Bornemisza built, in the last decades of the 18th century, the granary of the castle. The present-day castle was built in 1848, currently serving as local hospital. As a consequence of these remakes, from the 19th century onward, the local collective consciousness was confusing the Red Bastion with the birthplace of Gabriel Bethlen. In the years following 1850, the Red Bastion was rebuilt in the romantic style of the period, and after another remake at the turn of the 20th century, the modern commemorative stone was placed.
