When the city was defending itself from the approaching Assyrian army in the 8th century bce, King Hezekiah decided to protect the water by diverting its flow deep into the city with an impressive tunnel system.
This engineering feat was accomplished by digging a 1,750-foot (533
meter) tunnel into the mountain. Two teams started at the ends of the
tunnel and met half the way in. The slope has a height difference of
merely 30 cm from the beginning to the end.
This is 700 years before the Romans built their aqueducts! It is considered one of the GREAT mysteries/achievements of engineering of all times.
An ancient stone carving found near the entrance describes this incredible operation.
Featured in: jer-u-salem.tumblr.com/ (Nov 6, 2011)