It was built by order of D. João VI, in 1825 «for public use», as mentioned by the stonework pattern placed next to it.
The construction of the Santo Antoninho bridge was one of the works carried out when the so-called Estrada Nova was opened, connecting Punhete (now Constância) to the neighboring town of Abrantes. Thus, year-round traffic became possible, while until then the old Malvar road (Estrada do Campo), closer to the Tagus, was often impassable due to rains or even submerged by floods.

The bridge served until the middle of the 20th century, when the current EN 3 embankment was built to facilitate car traffic. Deactivated, it ended up being invaded by weeds.
Aware of its historical and heritage importance, the City Council of Constância began, in 1995, the process with a view to classifying it, which was recognized in 2010: Public Interest Group.

Public Interest Set.

Source: http://www.cm-constancia.pt/index.php/pt/visitar/patrimonio#ponte-de-santo-antoninho-conjunto-de-interesse-p%C3%BAblico