It has long been known that there is a pool inside the fort, but when the archaeologist Dr H. N. Savory excavated the hillfort between 1954 and 1956, he was surprised to find that not only were the fortifications of about the right time frame for either Vortigern or Ambrosius, but that there was a platform above the pool as described in the Historia Britonum.
However, he found the platform to date much later than the accepted floruit of either personage.

Savory described the fortifications as consisting of stone walls between 2.5 and 3 metres (8 and 10 ft) thick, which exploited every irregularity in the rocky hill-top, enclosing an irregular area of about a 10,000 m² (110,000 sq ft) in size.
The original means of access was by a steep path on the western side of the hillfort.
The present entrance from the north-east is a later addition.
The walls had been "poorly built of stone two or three times ", possibly inspiring the legend's reference to the building collapsing several times during construction.

The most conspicuous object currently on the hill is the base of a rectangular tower.
It is generally accepted that this is part of an undocumented castle built by the princes of Gwynedd in the eleventh century.
It has long been known that there is a pool inside the fort, but when the archaeologist Dr H. N. Savory excavated the hillfort between 1954 and 1956, he was surprised to find that not only were the fortifications of about the right time frame for either Vortigern or Ambrosius, but that there was a platform above the pool as described in the Historia Britonum. However, he found the platform to date much later than the accepted floruit of either personage.
Savory described the fortifications as consisting of stone walls between 2.5 and 3 metres (8 and 10 ft) thick, which exploited every irregularity in the rocky hill-top, enclosing an irregular area of about a 10,000 m² (110,000 sq ft) in size. The original means of access was by a steep path on the western side of the hillfort. The present entrance from the north-east is a later addition. The walls had been "poorly built of stone two or three times ", possibly inspiring the legend's reference to the building collapsing several times during construction.
The most conspicuous object currently on the hill is the base of a rectangular tower. It is generally accepted that this is part of an undocumented castle built by the princes of Gwynedd in the eleventh century.
Dinas Emrys