Dam spillway and kiln: what they have in common

1. Step 1. Dam spillway — is part of — Dam. It lets floodwater through.
2. Step 2. Dam — is made of — Roman concrete. Ancient dams; modern ones are made of concrete.
3. Step 3. Roman concrete — is made of — Lime. The binder is lime.
4. Step 4. Lime — uses — Kiln. Lime is made by burning limestone.

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