Some of the oldest walls in London are so called ‘rubble walls’, so not neat ‘dimension stone’ or ‘ashlar’ blocks which fit together so neatly like the Portland Stone that so many buildings in Westminster were built or faced with after the Great Fire of London, nor all the various styles of brick walls. The oldest rubble walls we can still see in London are in the Roman/Mediaeval London Wall and in the Medieval churches that still stand in villages that have been incorporated into London, which I’ll be covering in future. But this week I chanced upon a beautiful rubble wall at Mile End, by the lock, on the Regents Canal.
A rubble wall is built simply lumping whatever came to hand on top of each other in rough courses and bound by mortar. You can see this one needed patching up as different stones will have decayed faster than others. I can see granites, sandstones and limestones and possibly the places that have been patched would have been soft chalky ‘clunchs’.
This photo I’m guessing from the 1930s shows, I believe, the lock and Globe Bridge on Mile End Road, and note that almost all the buildings are now gone except on the left. 
The wall has a sign on it asking people not to graffiti and saying it’s been painted with anti-graffiti paint, as the wall is “100 years old”. But it’s probably twice that age.
Regents Canal was finished in 1820  and Mile End Lock and the line of the wall are there on maps of 1822  Note that canal ran literally around London often through what was still countryside and farms.
Most of Regents Canal was built with the yellow London Stock Bricks, using granite for edging the canal walls and I guess they just wanted something cheap for this wall, and would have got these from any demolition jobs of older buildings in London. It’s possible that some of this stone could be from Roman buildings in the City.
While the whole canal route is a local conservation area there is no mention of this wall anywhere I can see. 
References:  https://www.camdenwatchcompany.com/blogs/the-camden-watch-company/a-brief-history-of-regents-canal  https://www.gracesguide.co.uk/Regents_Canal  https://iiif.lib.harvard.edu/manifests/view/ids:8982541