Траян Көпірі: Төменгі Дунайдағы римдік сегменттік аркалы көпір

Roman segmental arch bridge over the lower Danube

Trajan's Bridge (Podul lui Traian; ), also called Bridge of Apollodorus over the Danube, was a Roman segmental arch bridge, the first bridge to be built over the lower Danube. Though it was only functional for 165 years, it is often considered to have been the longest arch bridge in both total span and length for more than 1,000 years. The bridge was completed in 105 AD and designed by Emperor Trajan's architect Apollodorus of Damascus before the Second Dacian War to allow Roman troops to cross the river. Fragmentary ruins of the bridge's piers can still be seen today.

The bridge was situated east of the Iron Gates, near the present day cities of Drobeta Turnu Severin in Romania and Kladovo in Serbia. Its construction was ordered by the Emperor Trajan as a supply route for the Roman legions fighting in Dacia. Construction of the bridge was part of a wider project, which included the digging of side canals so that whitewater rapids could be avoided to make the Danube safer for navigation enabling an effective river fleet, a string of defense posts and development of the intelligence service on the border. The remains of the embankment which protected the area during the construction of the canal (in a loop to the south of the Danube) show the magnitude of the works. The long canal bypassed the problematic section of the river in an arch like style.

Apollodorus used wooden arches, each spanning , set on twenty masonry pillars made of bricks, mortar, and pozzolana cement. It was built unusually quickly (between 103 and 105), employing the construction of a wooden caisson for each pier. Apollodorus applied the technique of river flow relocation, using the principles set by Thales of Miletus some six centuries beforehand. Engineers waited for a low water level to dig a canal, west of the modern downtown of Kladovo. The water was redirected downstream from the construction site, through the lowland of Ključ (oblast), to the location of the modern village of Mala Vrbica. Wooden pillars were driven into the river bed in a rectangular layout, which served as the foundation for the supporting piers, which were coated with clay. The hollow piers were filled with stones held together by mortar, while from the outside they were built around with Roman bricks. The bricks can still be found around the village of Kostol, retaining the same physical properties that they had 2 millennia ago. The piers were tall, wide and apart. It is considered today that the bridge construction was assembled on the land and then installed on the pillars. A mitigating circumstance was that the year the relocating canals were dug was very dry and the water level was quite low. The river bed was almost completely drained when the foundation of the pillars began. There were 20 pillars in total in an interval of Oak wood was used and the bridge was high enough to allow ship transport on the Danube. First idea was to leave the plaque at its position and to build the caisson around it but the calculations showed this wouldn't work. The idea of cutting the plaque in several smaller pieces in order to be moved was abandoned due to the quality of the rock of which it was made. The proposition of lifting it with the floating elevator "Veli Jože" was discarded, too. The motion of cutting the table in one piece and placing it somewhere else was rejected as the plaque would lose its authenticity. The superstructure was destroyed by fire. one in Romania and one in Serbia. In 1979, Trajan's Bridge was added to the Monument of Culture of Exceptional Importance, and in 1983 on Archaeological Sites of Exceptional Importance list, and by that it is protected by the Republic of Serbia.