The Newcastle Castle (the "New Castle upon Tyne") was originally built as a timber motte-and-bailey fortress in 1080. It was commissioned by William the Conqueror and constructed under the direction of his eldest son, Robert Curthose, after he returned from a military expedition against the King of Scotland. The fortress was strategically positioned on the site of a former Roman fort (Pons Aelius) to guard the bridge over the River Tyne and secure a passage for English armies into the northern territories. Because it was built on top of older Roman and Anglo-Saxon structures, it was dubbed the "New Castle," a name that eventually gave the city of Newcastle upon Tyne its identity. While the original 1080 structure was made of wood, it was replaced by a more formidable stone keep during the 12th century under King Henry II. Today, the surviving stone Castle Keep and Black Gate remain some of the finest examples of medieval military architecture in the United Kingdom, serving as a reminder of the site's 900-year history as a defensive stronghold.