Bike lane and barrel: what they have in common

1. Step 1. Bike lane — is a kind of — Paved road. A road.
2. Step 2. Paved road — has part — Mortar. Roman roads had layers set in mortar.
3. Step 3. Mortar — evolved into — Roman concrete. Roman concrete developed from lime mortars.
4. Step 4. Roman concrete — is material for — Amphitheatre. The Colosseum.
5. Step 5. Amphitheatre — has part — Arch. Arcades.
6. Step 6. Arch — works like — Barrel. Staves squeezed by hoops hold their shape by the same compression as the stones of an arch.

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