They didn’t need fancy computers, just a good eye and a steady hand. Romans used simple tools—groma for straight lines, a chorobates (a long wooden level) and the classic spirit level—to lay out a course that dropped about one to two centimeters per kilometer. That tiny, constant slope kept the water moving by gravity while preventing erosion. To keep it level, they built channels in cuts or on arches, constantly checking the gradient with a level. In short, a well‑measured drop over a long distance, checked with a few wooden frames, was enough to run an entire aqueduct.