Hadrian was the roman emperor codified laws and built a wall across Britain.
Explanation:
The Roman emperor named Hadrian built a wall across Britain which is known as the Hadrian's wall. The wall was constructed to fight for border between "Southern Britain and unconquered north".
It was known for the northern limits of Roman empire, and was constructed on the bank of river Tyne to Solway Firth on Irish sea. It is the largest "archaeological feature" in Britain and one the major tourist attractions too. It was also given the tag on UNESCO world heritage site.