Those stone ramparts were not rough guesses; they are hard geometry locked to the ridgeline. Each course tracks the crest, so runoff follows the natural watershed instead of cutting across it and gouging soil.
The real surprise is that the accuracy came from patient physics, not missing instruments. Builders used gravity surveying long before the term existed, rolling water along shallow test cuts and watching flow lines, then matching wall orientation to the observed hydraulic gradient so every gap became a controlled micro channel instead of a leak.
Modern dirt paths usually fail because they ignore that gradient and concentrate flow. Ancient ramparts diffuse it. Tight but not sealed joints act as a stone French drain, promoting laminar flow through the fill, while the wall crest stays just high enough above the ridgeline’s break in slope to shed water sideways before kinetic energy can build.