Paleorama[es] has an interesting article on how the Ancient Cantabrian castro (fortified town) at Monte Ornedo, located in the modern municipality of Valdeolea (Cantabria, near Palencia, Spain) was captured in fierce battle by the Roman legions in a key battle of the Cantabrian Wars, burned and on top of the remains a Roman fort was built instead (Octaviolca?)
The aboriginal castro covered 19 Ha (=190,000 m², ~47,000 acres), being the largest of its kind known in all Ancient Cantabria. Many brooches (fibulae), characteristic of the indigenous horsemen's clothing are concentrated near the main gate, suggesting that a key episode of the battle took place there. Around the castro, the Romans built their characteristic siege fortifications. Caligae sole nails, tent holding pins and weapons have been found all over the place, including a dagger with silver decorations and even a catapult fire projectile.
After the capture the Romans built there their own fort. First a campaign one with earth walls and then another more consolidated one with stone walls. Milestones defining the pastures assigned to the Legio IV Macedonica from those of the nearby town of Iuliobriga further North have also been found.