swisstone has spent years working on this country's Roman heritage, and it shows in his copiously detailed knowledge. He's made a point of paying attention to mentions in articles and guides of the visitable artifacts on the streets of London. This meant the tour included incidental material such as pieces of the medieval London Bridge, unlabeled in the church yard of St. Magnus the Martyr.
Our informal wander with a_d_medievalist started at the Museum of London, where we consulted with maps, models, and display cases. I admired a large surviving Roman ladder, realized how little I know about the Roman postal service, and was confused by case labels. ("I wonder what led to there being an Upper Thames St. in Whitby?" ) After a break for drinks, we headed out to explore the streets.
London has a number of medium-long stretches of surviving Roman wall, much of it the foundation for subsquent wall-building in the Middle Ages, and, after that, incorporated into houses. Much of the wall which is relatively intact, therefore, comes from houses damaged by bombing, or uncovered in excavations. A stretch in a hotel courtyard near the Tower of London was almost perfect, stone quarried in what is now Kent interspersed with tile coursing for lining up the horizontals.
The stretch of Roman wall by Tower Hill station.
Back to the beginning of the tour: the first stretch we visited bordered what was the Roman fort at the edge of the town, a structure which eats into the rough symmetry of the Roman walls.
A pass along Bassishaw Highwalk and more walls - now gardens and gaps along London Wall-the-street - and we looped around to the Guildhall, and the relatively-recently-discovered (1988) amphitheater underneath its courtyard.
This is a good wall for showing how the older walls were integrated into later buildings.
Eventually, we made it to part of the basilica, walking through Leadenhall Market, past neglected excavations of the structure.
After lunch, we part-closed the circle of the walls by walking the earthed-in waterfront, now a street in from the Thames, past a preserved structural timber of a Roman wharf, and the London Stone at what used to be St. Swithin's, and is now Cannon Street Station. We finished at the misplaced Mithraeum, moved and disoriented from its original excavation; the building it was moved to built will be torn down soon, and the Mithraeum may be replaced in its original location. (We thought of you, whatifoundthere!)
What remains of Roman London is more in absence than in presence: the roads which trace the course of where walls once were. Exvacations that have been filled back in with sand and tall buildings built over them. Few modern roads trace the routes of the Roman ones known to have been there. Yet the bones of Londinium still structure parts of The City, some of which are there for all who pay attention to see.