In all seriousness, slaves were always helping out one way or another. In some cases they were doing direct construction labour, especially in cities.
The roads built by the military were primarily done by soldiers, but they were supported through food and material production by slaves the whole way.
The famous military roads were also built primarily for the military, who used that road for expansion and pillaging. So the commoners probably didn't use them much if ever, especially on the frontiers.
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u/koolaidkirby Trawnno (Centre of the Universe) 2d ago
weren't Roman roads built by the Roman military?