Old London Bridge vs. Modern Thames Crossings: 600 Years of Engineering Evolution

For 622 years (1209–1831), Old London Bridge was the *only* dry crossing of the tidal Thames in London. Its replacement by modern bridges marks the shift from medieval urbanism to industrial metropolis.

Old London Bridge (1176–1209, stood until 1832)

• Structure: 19 irregular stone arches on starlings (pier foundations of rubble-filled caissons on gravel). Piers occupied ~80% of river width.
• Houses & Shops: ~140 structures, up to 7 stories, overhanging the roadway. Rent funded maintenance. A street *on* the bridge.
• Drawbridge & Gates: Central bascule (drawbridge) for tall masts. Stone gatehouses (portcullises, heads on spikes). Closed at curfew.
• Hydraulic Impact: Piers created a weir effect—5–7 ft water level difference upstream vs. downstream. Dangerous "shooting the bridge" for boats.
• Traffic: Narrow (12–15 ft between houses), one-way alternating, chronic gridlock. Carts, herds, pedestrians.

Modern Bridges (Tower, London, Millennium, etc.)

• Materials: Steel, concrete, pre-stressed, cable-stayed, suspension.
• Clearance: High fixed spans (Tower Bridge: 140 ft bascules open) or sufficient air draft—no mast lowering.
• Capacity: Multi-lane vehicle, dedicated cycle/pedestrian, sometimes rail (rail/road combos).
• Foundations: Deep caissons, piles to London Clay/Chalk. No starlings.
• No Housing: Pure transport corridors.
• Hydraulics: Minimal flow obstruction. Piers aligned with current.

The Transition

New London Bridge (Rennie, 1831)—5 granite arches, no houses—replaced Old. Itself sold/rebuilt in Lake Havasu, AZ (1971). Current London Bridge (1973) is a concrete box girder. The medieval anomaly is gone; the river flows freely.