This episode is a love letter- a literal sonnet- to one of the most hidden parts of London I know. I've never seen this in any guidebook or website- I only heard about it through word of mouth. If you want to find it for yourself, you'll first have to find your way into the underground London Wall Car Park. The entrance is hidden round a weird bend in the road and under a bridge. Then you'll have to go all the way down to Bay 51, which takes a good ten minutes on foot. I believe this is the largest chunk of the Roman wall still standing. There are larger chunks on either side of London Wall road and near Tower Hill station, but although they stand where the original wall once stood, the actual fabric of those is medieval and Victorian. You can tell this is Roman because of its distinctive tile-stone-tile stripes. The first wall around London (or Londinium as it was called by the Romans) was built c.120AD of wood. It was rebuilt in stone around 200 AD.