The Romans Never Conquered the Northernmost Region

Rome had conquered much of modern day england, but the native celtic tribes continued to resist. The romans eventually realized that a regional base in the south wasn't going to be enough if they wanted to conquer the entire island. After several decades of hard fighting, the romans were finally able to subdue the tribes in wales as well as the tribes in some of the northern portions of britain. In fact, the later emperor hadrian built the now famous hadrian's wall across northern britain to establish the limits of roman occupation and to protect it against those tribes to the north.