Short answers, pulled from the story.
The Pons Fabricius, built in 62 BC during the late Republic, is the oldest Roman bridge still intact and in use today. It stands in Rome and has been in continuous service for over two thousand years.
Trajan's Bridge over the lower Danube was built by Apollodorus of Damascus and remained the longest bridge in the world for over a millennium, measured by both overall length and individual span. It featured open-spandrel segmental arches of wood resting on concrete piers 40 metres high.
The Romans built three main types of bridges: wooden, pontoon, and stone. Stone bridges were the most enduring and used the arch as their primary structural form. Colin O'Connor's survey lists 330 Roman stone traffic bridges, 34 timber bridges, and 54 aqueduct bridges.
Opus pontis, meaning bridge work, was the term for the costs of building and maintaining Roman bridges. These costs were shared across multiple local municipalities rather than paid by any single town. The Alcantara Bridge in Lusitania, for example, was financed by 12 local municipalities, whose names were inscribed on the structure.
The longest surviving Roman bridge is the Puente Romano at Merida, measuring 790 metres. The longest known surviving Roman stone arch is the Severan Bridge in Türkiye, built around the year 200, with a maximum span of 34.2 metres.
Roman engineers built stone bridges by first constructing cofferdams, watertight enclosures pumped dry with buckets, to lay foundations in riverbeds. All foundation work was done during the dry season. Arches were assembled on temporary wooden frames, with the keystone as the final block that locked the structure together once the frame was removed.