This bridge was constructed at the end of the 1 st century or beginning of the 2nd century, by engineers under the emperor Trajan.

CHAVES
Aquae Flaviae was the principal municipium civitas in the northwest (from epigraphic findings) implanted in the Trás-os-Montes, on a small hill on the banks of the River Tâmega, in the Roman province of Gallaecia. This was a fertile area, where hot springs abound, in addition to a mining region from which gold is extracted. It is also located in a strategic place between the Roman cities of Bracara and Asturica, as well as the mining districts of Três Minas and Jales, located southwest of the civitates.
Architecturally, the most notable feature of this city, is the bridge of Trajan over the Tâmega River, whose existence marked a period of exceptional development of the city. Functioning as a crossroads, it controlled the routes to the mining districts. The remains of two epigraphic inscriptions are located on the bridge, commemorating the construction or remodeling by Emperor Trajan, and was in full use for motor vehicles until ca. ten years ago . . .