Hierapolis sawmill and tunnelling shield: what they have in common

1. Step 1. Hierapolis sawmill — has part — Water wheel. Driven by water.
2. Step 2. Water wheel — is part of — Gunpowder mill. The drive.
3. Step 3. Gunpowder mill — uses — Gunpowder. Production.
4. Step 4. Gunpowder — evolved into — Dynamite. A replacement for gunpowder in mining.
5. Step 5. Dynamite — works like — Tunnelling shield. Two ways of driving tunnels — mechanical and explosive.

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