The Drosgl mountains are a location that appears in The Roman Film. They are a large area of rocky terrain in the Celtic lands, but were heavily quarried by the Romans after their invasion of the realm. They are most well-known as the location of the Cave the Dragon was imprisoned in.
After the Dragon emerged and destroyed many of the tribal villages (As appear in the Roman Prequel), the Dragon meved to these mountains as its home. The Alliance of Druids tracked the dragon to here and used the freshly-forged Staff to battle the dragon. Gwydion used the staff to control the dragon and force it into the Cave, which he later sealed by collapsing a rock face onto the opening. Shortly after this, the Ice Age began in the area, and the whole mountain froze over. over a hundred years, glaciers crunched against the sides of the mountain and eventually scratched the surface until a narrow and deep tunnel formed leading into the Dragon's prison below. The Celts and Gwydion were well aware of this, but kept it a secret from the Romans, knowing that one of them could easily be crazy enough to try to venture inside. Magnus Maximus was.
Magnus Maximus ordered scouts to search all around Britannia after hearing of the existance of the Cave, hoping to find the location the Dragon was trapped at. He planned to use the Staff to tame the Dragon after releasing it, so it could be used to kill Claudius and take over the Roman Empire. Unfortunately/fortunately, the dragon resisted Magnus's lack of magic skills and rampaged around the mountain, dessicating the Roman Army stationed there. The ground of the mountain was burnt and the entire cave system collapsed during the Dragon's explosive escape. When Gaius managed to turn the Dragon to stone using the Staff, it became fused with the rock of the mountain and remained as a permanent rock structure.