The viaducts and aqueducts is one of the main reasons Roman citizens stayed alive. The Greece and Roman citizens needed the water supplies along with the goods they transported. The citizens would have had way less resources if it wasn't for the aqueducts.
The viaducts and aqueducts were a major contribution because it was the romans main water source. Without these the Roman citizens would have ended a lot sooner. Water and resources were transported through these and without them it would have been very hard to stay healthy and alive.