Dinas Emrys (Welsh for "fortress of Ambrosius") is a rocky and wooded hillock, forming a landmark above the valley floor near Beddgelert in North Wales. While it is of interest to archeologists because it is an example of a hill fort whose fortifications entirely postdate the Roman period, this hillock is of interest to the greater group of enthusiasts about the legends of King Arthur. This is the setting of the famous exchange of the warlord Vortigern and the youthful Ambrosius Aurelianus, as told in the Historia Britonum; Vortigern, following the advice of his councillors, was planning to kill the boy in order to appease supernatural powers that prevented him from building a fortress here; Ambrosius laughed at this advice, and instead explained that the hill fort could not stand due to a hidden pool containing two vermes, a word that can be translated as either "badgers" or "dragons".

It has long been known that there is a pool inside of the fort. But when the archeologist Dr H. N. Savory excavated the hill fort between 1954-6, 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 florit of either personage, showing that the story was not entirely accurate. The question of whether the existence of the platform near the pool or cistern inspired the story, or the platform was built in response to the story has not been determined.

Savory described the fortifications as consisting of stone walls between 2.5 and 3 metres thick, which exploited every irregularity in the rocky hill-top, enclosing an irregular area of about a 10,000 m² in size. The original means of access was by a steep path on the western side of the hill fort; the present entrance from the north-east is a later addition.

The most conspicuous object currently on the hill, the base of a rectangular tower, is part of an undocumented castle, most likely built by the Welsh in the twelfth century.

Bibliography

• H. N. Savory, Arch. Cambrensis, 109 (1960), 13-77.