The Romans built ~80,000 km of roads. Not because they loved roads, but because empire requires logistics, and logistics requires infrastructure.
The road network made possible: rapid troop movement, the cursus publicus (state postal service), commercial integration of a territory spanning from Scotland to Mesopotamia.
When the Western Empire collapsed, the roads didn't disappear — they continued to be used for centuries, slowly degrading without maintenance. The "Dark Ages" in part means "the era when nobody could maintain Roman infrastructure."
Related: logistics-wins-wars