We are in the year 10 (CE), under the reign of Emperor Augustus. You are an architect in a prosperous city and the council has just hired you. The wooden bridge that spanned the river was washed away during the last flood. The city is rich and the job that the council gives you is to rebuild a stone bridge.
Building a large stone structure is constraining. A large stone slab is heavy and it would break under its own weight. You have thought about multiplying the columns between each slab, but it would be as many obstacles to navigation. It is these same constraints that forces the use of multiple columns for the stability of temples such as the Parthenon of Athens or the temple of Apollo of Pompeii.
Why not consider an arch structure? The Æmilius Bridge in Rome built in 179 BC. is an engineering feat that celebrates in its own way the glory of Rome. All major projects now include vaults: Whether for a palace, an aqueduct, an arena, a basilica, a bridge or thermal baths, all the cities of the empire must integrate arches and domes, especially to mark the entrances to the city and impress visitors. Huge triumphal arches will even be built to honor great victories.