The Royal Citadel (tr. Kral Saray), also known as the Great Castle (tr. Büyükkale), was, as its name suggests, the seat of the Hittite kings. Because of its location, at the highest point of the Old Town, it offers stunning views of the whole area of Hattusa but also the valley in the north where the modern Turkish village of Boğazkale is situated.

The earliest traces of settlement found in this area come from the Early Bronze Age, but most of the visible remains of the buildings date back to the 13th century BCE. In this period, a large-scale redevelopment project of Hattusa was carried out, including the restoration of the ramparts.

A huge viaduct led into the interior of the Royal Citadel, reaching its South Gate - the main entrance to the complex. It was once adorned with two sculpted lions, similar to those of the Lios Gate. Currently, the area of ​​the Royal Citadel can be reached by climbing modern stairs.

The citadel consists of a system of interconnected courtyards, archives, living quarters, religious buildings, and the audience hall. The whole palace complex was surrounded by ramparts. It occupies the top of a hill, and its area is 250 meters long and 140 meters wide.

Within the Citadel the remains of the Hittite Empire archives have been found. It is the oldest known building designed and built as a library. In its heyday, it had two floors and consisted of four rooms. On its site, archaeologists discovered more than 3,000 clay cuneiform tablets. After they had been analyzed, it turned out that they contained not only formal agreements, verdicts, and documents, but also predictions, worship instructions, descriptions of the customs and folklore, and historical texts.

In another room at the Citadel, 'the Treaty of Brotherhood and Peace of Kadesh' was found in 1904. The pact was signed after the Battle of Kadesh, fought around 1,280 years BCE, between the Hittite king Hattusilisem III and the Egyptian Pharaoh Ramesses II.

The visit to the Royal Citadel may be somewhat disappointing to some of the tourists as very few traces remained to give evidence of the former power of the Hittite kings. Many visitors feel lost in the area of the Citadel because its ruins cover a large area and consist mainly of low walls and the scanty remains of ancient buildings. It is worth remembering that the area of ​​the Citadel had been thoroughly investigated by archaeologists, but many structures discovered there were again covered with soil to protect them from destruction.