A row of brick houses from the last century, shutters and stone door frames, a narrow lane between them.
Look under the walls and there is daylight.
The whole block sits on a steel grillage, and the grillage sits on hundreds of squat hydraulic feet.
It is going somewhere, at roughly the speed of a slow walk spread across an entire day.
The load per foot is about 10 tons.
Which is not the hard part, and never was.
Why walking beats rolling for this job
The old way to move a building is rollers or rails. That needs a straight prepared track, and it only goes one direction.
These feet work differently. A group of them takes the load, the rams push the frame forward a short step, the feet set down, and the next group lifts.
Because each foot can be driven in any direction, the whole assembly can turn and change heading without laying new track.
That is the only reason this was possible at all, in lanes too narrow for a crane and a courtyard plan that had to travel two ways.
But the real problem is not carrying the weight. Brick and timber will not tolerate differential settlement.
Let one corner drop a fraction of an inch relative to another and the mortar joints open, which is why the engineering here is synchronization rather than lifting.
What is under there and what it is holding
The building is a shikumen complex in the old quarter, put up in the 1920s and 1930s.
Shikumen is a hybrid form, a Western terraced row wrapped around a Chinese courtyard, with a carved stone gate at the front.
The floor area is around 43,380 square feet and the whole thing weighs about 8,270 tons.
Under it sit 432 walking robots, each a modular hydraulic jack that can travel in any direction.
Four hundred and thirty two small feet rather than a dozen large ones is a deliberate choice. No single point takes a heavy share.
Sensors on the frame read pressure, vibration and alignment continuously, and a central controller keeps every foot inside the same envelope.
The two trips and what they took
The block did not move once. It moved out, waited more than a year, and then came back to almost exactly where it started.
The outbound leg ran in late 2023 and displaced the whole complex 157 feet west and 151 feet north.
Then it stood aside for well over a year while a very large hole was dug where it had been standing, with the complex parked on its feet the whole time rather than propped on cribbing.
The return began on the nineteenth of May last year and finished on the seventh of June, nineteen days from start to stop.
At roughly 33 feet a day, which is a pace chosen for the mortar rather than for the hydraulics.
The date sometimes given as the tenth of May is the wrong one, and the nineteenth is what the record shows.
What the hole was actually for
Preservation is the headline and it is genuinely part of it. The complex carries heritage protection and demolition was never on the table.
But nobody spends this to save a facade alone. Underneath now sits roughly 570,500 square feet of shopping floor, parking and subway connection.
The building is the lid on that, and the lid had to be lifted off and put back.
Moving structures whole is not new, and the same logic scaled down puts a frame house on wheels and off its lot in a morning.
At the other end of the scale it is how a dragline crossed miles of open pit after being jacked up and set down on transport.
What separates this job from both is that the cargo was never designed to be lifted at all.
What has not been published
The numbers that would settle whether this worked are exactly the ones nobody has released.
No crack survey before and after. No settlement log. No record of how far out of level the frame ever drifted during the walk, and no note of whether any foot ever had to be taken out of the sequence.
For a building whose failure mode is a fraction of an inch, that is the interesting file and it is not public.
The detailed account covers the hardware and the schedule and stops there.
What is clear is the economics. Moving a protected block is now cheaper than losing the land under it, which is a specific claim about property values rather than a general one about preservation.
Where the ground is worth less, the same block gets a demolition permit instead.
