The aqueducts were constructed by the ancient Romans around 145 B.C. and were used to bring in water for the Roman Empire. The really fascinating part? The aqueducts work on gravity alone, meaning that the design is what allowed the water to be siphoned. This is one of the earliest examples of engineering and quite an impressive one at that, especially considering the lack of resources available at the time. The aqueducts still stand intact today. Many were long lost and forgotten, taken over by shrubs and vines, but many are still visible in the same form they were thousands of years ago.