From the World Heritage inscription:
Speyer Cathedral exerted a considerable influence not only on the development of Romanesque architecture in the 11th and 12th centuries, but also on the evolution of the principles of restoration in Germany, in Europe, and in the world from the 18th century to the present.
The cathedral, along with those of Worms and Mainz, is a major monument of Romanesque art. It is, by virtue of its proportions, the largest, and, by virtue of the history to which it is linked (the Salic emperors made it their place of burial), the most important.
The cathedral, dedicated to St Mary and St Stephen, was founded by Conrad II and was built essentially between 1030 and 1106. It incorporates the general layout of St Michael of Hildesheim and brings to perfection a type of plan that was adopted generally in the Rhineland. This plan is characterized by the equilibrium of the eastern and western blocks and by the symmetrical and singular placement of the towers which frame the mass formed by the nave and the transept. Under Henry IV renovations and extensions were undertaken.
Speyer Cathedral is the first known structure to be built with a gallery that encircles the whole building. The system of arcades added during these renovations was also a first in architectural history.
Speyer Cathedral is the largest romanesque cathedral in the world and is the burial site for eight different German emperors and kings.
Despite its romanesque origins, there are many additions to the cathedral which have changed its original design, including 18th and 19th century extensions to the facade and towers.
The interior of the cathedral is shockingly bare with most of the original artwork and paintings gone. Renovations have cleaned the interior stone to such a degree that the it almost looks new, despite some of it being almost 1,000 years old.
One unique tradition you’ll find at Speyer is the large bowl (domnapf) in the front of the building near the plaza. That used to mark the boundary line between the church’s property and the city. When a new bishop was installed, the bowl was filled with wine and everyone in the city could drink freely. The tradition remains today, except you now have to purchase a cup to get access to the free wine.
The original design of the building was based on St. Michael’s Church in Hildesheim, which is also a world heritage site.
Speyer Cathedral is located in close driving distance to the Messel Fossil Pit and Abbey of Lorsch world heritage sites.