In brief
The cathedral combines clearly longitudinal space, towers and domes in a monumental composition.
Useful to know
The cathedral at Speyer was begun in 1030 under Conrad II and was revised towards the end of the 11th century. UNESCO presents it as an important example of Romanesque architecture: a basilica with four towers and two domes. It is also associated with the burials of German emperors. [1]
For architectural observation, compare the longitudinal body with the vertical accents. Massive volumes are not just the background of the decoration; through them the building declares scale and public importance. The rhythm of the repeating parts helps to read the length of the space.
Don't reduce the Romanesque style to the definition of "heavy walls." In Speyer there is an organized composition of different volumes, which can also be viewed without detailed knowledge of the dynasties. The date of commencement is a landmark, but it does not mean that everything visible is built at once.
Sources
For further detail and to check the information: