Decades ago, children would play in the caves and tunnels under the hill of Posillipo in Italy. They would run and duck through the subterranean world, weaving through miles of underground tunnels. When the now-grown adults told stories of the tunnels to researchers, they were puzzled, LiveScience reported.

Italy has a rich history of underground aqueducts built by the Romans to move water throughout their cities. The structures have continued to baffle modern architects for their strength and ingenuity. But, most of the aqueducts that have been studied exist in Rome, not in sprawling cities like Naples.