The London & Birmingham Railway’s engine house of 1837, sixteen-sided round a turntable, is the earliest known railway roundhouse. It was demolished around 1860 and found again by HS2’s archaeologists.
The roundhouse — outline from the HS2 excavation (checked against the 1855 plan); 16 sides and a domed roof by 1843 from the excavation report (height estimated)Landmarks standing todayCurzon Street station’s entrance building (1838) — survives, Grade IBuildings today (OpenStreetMap)