History
Strategies Behind the Construction of Roman Aqueducts
Quick fact
The aqueducts of Rome had a total length of over 500 kilometers, but only a small fraction was visible arches; the rest ran underground, tunneling through hills and following gentle slopes over long distances.
Why this is interesting
Imagine millions of gallons of water flowing daily into ancient Rome—without a single pump. How did they make water flow uphill, across valleys, and through mountains, all using only gravity?