Danube
The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world. Ordered from the source to the mouth they are:
The Danube is navigable by ocean ships from the Black Sea to Brăila in Romania and by river ships to Kelheim, Bavaria, Germany; smaller craft can navigate further upstream to Ulm, Württemberg, Germany. About 60 of its tributaries are also navigable.
New Europe Bridge
The Danube Bridge 2 consists of eight pillars that are in the non-navigable channel of Danube river, crossing from the low lying Bulgarian bank over the small island, followed by its four main pillars, numbered PB9, PB10, PB11 and PB12. The design was to have 13 pairs of stay cables attached to every main pillar in the navigable channel of the Danube river.