The German construction number (Bauwerksnummer) is a 7-digit identification key issued by the government to infrastructure objects throughout Germany. It consists of a 4-digit prefix identifying the map tile where it is located, followed by a sequential 3-digit number.

The map tile is the sheet of the German topographic survey at 1:25,000, so the prefix places the structure geographically and two objects far apart never share it.

It covers engineering structures such as bridges, tunnels and retaining walls rather than ordinary buildings, which is why most records carry none.

The sequential part restarts within each tile, so the last three digits identify nothing on their own and the number has to be kept whole.