The crown is a larger-than-life replica of one in the treasury of the Cathedral.
The original crown belonged to the Salian dynasty of Holy Roman Emperors.

Conrad II, the first Salian emperor, began work on the Dom in 1030. The cathedral was the largest cathedral in the world when it was first built.
Even in its current state of reconstruction, the cathedral is a great example of the Romanesque style and beatiful in its simplicity and scale.