Petra
About
Nabataean engineers built this dam across the Siq's mouth around the mid-first century BCE, sealing Petra's main entrance from flash floods and diverting water through a tunnel cut nearly 90 meters through rock. Standing about 13 meters high, it protected the processional approach for centuries. Trajan annexed the Nabataean kingdom as Arabia in 106 CE, just eleven years before this map's snapshot, so by 117 CE the dam guarded a new Roman province rather than an independent kingdom.
What happened here
Built to hold water for a town, a farm or a mine, and shaped by what the local rock allows: a straight wall of masonry backed with earth, or a curved one where the gorge is narrow. The core is concrete and rubble, faced in cut stone, and the upstream face is often waterproofed with mortar. Water is drawn from a tower with sluices at different heights, so the supply keeps running as the level drops and the silt stays at the bottom. Overflow channels carry the winter flood past the wall rather than over it — the detail that decides whether a dam survives. Silt is the long enemy; a reservoir has a working life and everybody involved knows it.
Sources
Roman Maps shows the empire frozen at 11 August 117 CE, the day Trajan died — its moment of greatest territorial extent. Explore the full map →