The railway bridge in Fronołów is a railway bridge in the village of Mierzwice-Kolonia on the Bug River, on the Siedlce-Czeremcha railway line, between the Fronołów and Siemiatycze stations. It was built between 1904 and 1906, designed by Lavr Proskurjakov.
It is a truss bridge with a riveted steel structure and three spans. It consists of two parallel passages allowing for grade-separated traffic in both directions, although initially one of the passages was used only for vehicular traffic. The total length of the bridge is 294 meters, and each span has a span of 98 meters. Upon completion, it was one of the largest railway bridges in the Kingdom of Poland.
In 1901, the Tsarist authorities decided to build a railway line from Siedlce to Polotsk. The main reason for building this line was Russia's fulfillment of agreements with France, which would allow for the efficient transfer of troops from the three military districts: St. Petersburg, Moscow, and Kazan to the western borders of the Russian Empire. The Bug River was, next to the Neman, the largest water obstacle along the entire route, necessitating the construction of a robust crossing there. Construction of the Siedlce–Polotsk railway section was led by communications engineer Vladimir Timofeyev-Ryasovsky. Almost all the equipment, including the rails, came from Russian factories. Local workers were employed in the construction work.
The bridge was built according to the design of architect Lavr Proskuryakov, who had previously designed the Trans-Siberian Railway bridges on the Yenisei in Krasnoyarsk and on the Amur in Khabarovsk. The steel components of the bridge were manufactured by the K. Rudzki i S-ka Joint-Stock Company factory in Mińsk Mazowiecki, while the chief engineer was a Russian engineer. Aleksy Aleksander Lubicki, in later years the builder of the Poniatowski Bridge in Warsaw.