Aqueduct

View looking down from the acropolis of Machaerus, southeast, at the remains of the aqueduct that brought water to the palace/fortress of Machaerus.

The straight line of the (foundations of the bridge of the) aqueduct runs from the top center of the image straight toward the lower center of the image.  Water from the aqueduct would have filled the cisterns at Machaerus. 

Roman aqueduct technology was such that they could propel water through low areas, and even to heights.  See the commentary from the aqueduct at Aspendos in Turkey .

The path on the right (west) side of the image is modern that leads from the car park to the top of Machaerus.

This image courtesy of Mark Connally.