The celts built, what could best be called trails and in some cases improved trails, in today’s lingo.
The Romans built solid lasting road structures. Sometimes over those trail (roads) sometimes not.
Every culture and every period of mankind has created whatever “roads” the peeps felt needful or could afford. In most cases, though, the “roads” were not much more than trails cut through the foliage with dirt compacted by traffic.
Paths worn by goats and other animals were followed by cave men who later widened them and developed them as trails under the city-states and then cleared them wider for wagons and on and on. Eventually they were transformed into superhighways.