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Environment Agency LiDAR shows the land under the Square Mile: Ludgate Hill, Cornhill, the lost Walbrook and the Fleet valley, plus a walk to feel it.

Colour relief map of the City of London's bare ground, buildings removed, with the City boundary in white. Two raised areas in orange and red are labelled Ludgate Hill and Cornhill; a dark blue valley in the west is labelled Fleet valley; the River Thames runs along the bottom.Explainer: aircraft LiDAR measures heights; the Environment Agency filters out buildings to leave bare ground. A colour bar runs from blue at 5 m to red at 19 m above sea level.Close-up relief of Ludgate Hill with St Paul's marked on the high ground and the Fleet valley to the west.Close-up relief of Cornhill, the eastern hill, with Bank marked to its west.Relief with colours stretched from 9 to 18 m, showing a blue-green trough running north to south between St Paul's and Cornhill, labelled Walbrook, with the Temple of Mithras marked on its bank.Relief of the Fleet valley: a deep blue channel running south past Farringdon Street, about 10 m below St Paul's, with Holborn Viaduct and St Paul's marked.Closing card: "The ground remembers what the streets forget". Follow @cityoflondon for weekly London plans and the stories under your feet.

7 slides. Swipe or scroll sideways. .

Strip away the towers and you can still see the shape of the land the Romans chose: two low hills with a stream between them, and a deep river valley to the west.

📍 Ludgate Hill: about 17 m above sea level, with St Paul's on top
📍 Cornhill: about 18 m, where Roman London's forum and basilica stood
💧 The Walbrook: the lost stream between the hills. The ground around Walbrook is still 4 to 5 m lower than the hills.
💧 The Fleet: at Farringdon Street the ground is about 10 m below St Paul's

Walk it: start at St Paul's, head east along Cheapside and feel the slope down to Bank, then climb Cornhill.

Heights are our own readings of the Environment Agency's 1 m LiDAR terrain model (buildings filtered out), smoothed to show the shape of the land. LiDAR: © Environment Agency copyright and/or database right 2022. All rights reserved. Open Government Licence v3.0. Boundary: © OpenStreetMap contributors.

Send this to someone who walks past St Paul's every day.

Slide by slide.

  1. Colour relief map of the City of London's bare ground, buildings removed, with the City boundary in white. Two raised areas in orange and red are labelled Ludgate Hill and Cornhill; a dark blue valley in the west is labelled Fleet valley; the River Thames runs along the bottom.
  2. Explainer: aircraft LiDAR measures heights; the Environment Agency filters out buildings to leave bare ground. A colour bar runs from blue at 5 m to red at 19 m above sea level.
  3. Close-up relief of Ludgate Hill with St Paul's marked on the high ground and the Fleet valley to the west.
  4. Close-up relief of Cornhill, the eastern hill, with Bank marked to its west.
  5. Relief with colours stretched from 9 to 18 m, showing a blue-green trough running north to south between St Paul's and Cornhill, labelled Walbrook, with the Temple of Mithras marked on its bank.
  6. Relief of the Fleet valley: a deep blue channel running south past Farringdon Street, about 10 m below St Paul's, with Holborn Viaduct and St Paul's marked.
  7. Closing card: "The ground remembers what the streets forget". Follow @cityoflondon for weekly London plans and the stories under your feet.
Sources (10)
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