“WOW”
I’m with you. The ability of them to build aquaducts for hundreds of miles, or even this dyke for 70 miles is amazing, considering they have to get the slope just right (i.e., too little and the water pools or spills over, too much and they quickly run out of vertical drop to use. And then the weight and subsidence issues - WOW!. And this is based on my experience in trying to lay 100 feet of 4” PVC drain line...not as easy as it looks.
They had a lot of experience with water handling in the form of gravity-fed (rather than pressure-fed) aqueducts and inground sewer systems that didn’t clog.