The foundation of the diocese is closely connected to the legend of the Thousand-Year-Old Rose Tree. The mighty rose bush climbs up the exterior wall of the Cathedral´s apse and is a landmark of the diocese and the city of Hildesheim.

The legend has it, that Ludwig ´the pious´ and his entourage lost their way while they were hunting. In the vicinity of what is now Hildesheim he ordered a rest and had a mass celebrated, in order to pray for his rescue.
For the mass a reliquiar of Holy Mary was hung into a bush for worship. When the danger was finally averted, the servants forgot to retrieve the reliquiar. When its missing was later noticed, Ludwig and his group returned, but the reliquiar turned out to be irremovably connected to the bush. Ludwig interpreted this as a divine sign, built a chapel for Holy Mary, and thus founded the diocese of Hildesheim.

The founding reliquiar, the so-called ´Lipsanothek´, can still be viewed in the Cathedral´s treasure today. It is a 9th century karolingian capsule, which is said to contain remains of both Holy Mary and Jesus Christ.

The Thousand-Year-Old Rose Tree, as the plain dog rose (lat. rosa canina L.) is called, was highly revered throughout all times. After the devastating bombardment in the noon hours of March 22, 1945, the Rose Tree was buried under large pieces of the Cathedral´s apse. But the rose was not destroyed. Instead the apse´s pieces protected its roots from burning. Two weeks after the bombardment the Rose Tree began to blossom again. Up to today these events play an extraordinary role in Hildesheim.