Coming out of Gilsland there is a section of Hadrian’s Wall that was built as “narrow wall” (eight Roman feet wide) on top of “broad wall” (ten Roman feet wide). As the narrow wall is later in date, this indicates that the foundations were built first and the main wall was built afterwards.
Further on there is a milecastle.
The wings of the milecastle that join into the wall are also built as broad wall and are stepped in to meet the inner face of the narrow wall. This indicates that the mile castles were built independently and before the main wall.
Further down there is the remains of a bridge abutment. This was significantly modified twice throughout its life as it was presumably damaged by by the river. To relieve pressure on the structure sluices were put into the wall on the first rebuilding.
As these seemingly didn’t prove sufficient they were widened when it was modified for the second time.