Several excavations have shown that sections of the wall were constructed at different times and in various ways that differed from the uniform construction of the landward wall. Some sections seem to have been built in the late 3rd century while others may have been built at some time in the late 4th century.
A section of riverside wall found at the Tower of London showed that the wall was modified here in the late 4th century. The lack of consistency in the construction of the riverside wall by comparison with the earlier landward wall, suggests that it may not all have been built at the same time.
However, it is known that it was gradually destroyed by river action, which undermined its foundations and by the 10th and 11th centuries it had collapsed. FitzStephen, a 12th-century historian, tells that “on the south London was once walled in and towered in like fashion, but the Thames, that mighty river, teeming with fish, which runs on that side with the sea’s ebb and flow, has in course of time washed away those walls, undermined and overthrown them”.
In 1974-5, excavations uncovered a massive collapsed length of wall at Blackfriars with two styles of wall construction. In the eastern part there was a 40m length of wall, built of ragstone with tile courses constructed in a similar (but less precise) manner to the landward wall (BC75). Its foundation was of a row of oak-piles rammed into the underlying gravel, with a thick layer of chalk above. Reconsideration of the dating evidence from the oak piles has suggested the late 3rd century for the construction here.
In the western part, the riverside wall had no elaborate foundation, simply large ragstone blocks rammed into the clay. It had token tile courses on the inner face only and it contained stone blocks of re-used stonework from a demolished monumental arch and screen of late 2nd to 3rd-century date, and inscriptions that dated to the mid 3rd century. The re-used stone suggests that it may have been built hurriedly in a time of crisis at some time in the 4th century.
In 1977 and 1978, excavations within the Tower of London exposed the eastern end of the wall just inside the Inner Curtain wall of the Tower. Here the original wall had been either rebuilt later, further to the north, or a secondary wall had been built while the original wall was still standing.
This later wall however, did not continue in a straight line to the east, as did the original wall in order to meet the landward wall, but turned south at an angle. The reason for building such a defensive promontory is unclear. The later wall had slight foundations built of clay mixed with flint, ragstone and chalk, and was faced on its northern side with neatly-squared blocks of stone. The outer face consisted of ragstone with one double course of tiles. Abundant coin evidence from below a clay bank supporting the rear of the wall indicated that it had been built at the very end of the 4th century.
For details of what can be seen today, go to Riverside wall in Londinium Today.