The Design Evolution of London Bridge: From Roman Pontoon to Concrete Box Girder

The current London Bridge (completed 1973) is a study in pragmatic modernism: a three-span, post-tensioned concrete box girder, 928 ft (283 m) long and 62 ft (19 m) wide, with five lanes of traffic and pedestrian walkways. But its design lineage spans two millennia.

Key Design Milestones

• Roman (50 AD): Timber piles/pontoons at the lowest tidal crossing. Pure utility.
• Medieval (1209): 19 irregular stone arches with starlings (pier protections). The bridge was a street—shops, houses, chapel, latrines overhanging the river. A vertical village.
• Rennie (1831): Five semi-elliptical granite arches, 150 ft span each. Classical elegance, engineered for river flow. No buildings—just a bridge.
• Current (1973): Three-span continuous concrete box girder (central span 340 ft). Minimal piers for navigation. Granite cladding for aesthetics. Bascules (lifting leaves) retained for ceremonial/rare vessel passage.

Design Details (Current Bridge)

• Length: 928 ft (283 m)
• Width: 62 ft (19 m)
• Piers: Two main river piers, 100 ft wide × 70 ft high
• Ornament: Polished granite facing; subtle dragon/griffin motifs on pier caps (nod to City of London heraldry)
• Traffic: >50,000 vehicles/day

Philosophy Shift

From a place (medieval bridge-as-street) to a link (modern bridge-as-infrastructure). The current design prioritizes flow—of traffic, water, pedestrians—over habitation. It's a bridge that does one thing exceptionally well: span the Thames at its historic heart.