As we're seeing with infrastructure now in the US, civil engineering isn't a "do once" kind of job. Infrastructure (roads, bridges, irrigation etc) takes consi

As we're seeing with infrastructure now in the US, civil engineering isn't a "do once" kind of job. Infrastructure (roads, bridges, irrigation etc) takes consistent upkeep, resources, and redesign as the fixtures degrade and usage patterns change. Engineers still need resources, manpower and direction, so as the empire's control area and wealth centralization receded, so did the impetus/capacity to maintain infrastructure.