The Jewish communities of Mainz, Worms and Speyer are known together by the acronym ShUM, formed from the Hebrew initials of the three city names. From the tenth century they held the leading rabbinic academies of northern Europe, and what was decided in them shaped Ashkenazi law, liturgy and custom for centuries afterwards. The ban on polygamy attributed to Rabbenu Gershom of Mainz, the commentary tradition that Rashi carried back to Champagne after studying on the Rhine, and the Tosafist habit of reading the Talmud through its own contradictions all belong to this milieu.
The communities were destroyed and rebuilt more than once. In the spring of 1096 armed bands moving east ahead of the First Crusade attacked the Rhineland communities in turn, and large numbers were killed or died at their own hands rather than accept baptism. Jewish chroniclers recorded the events within a generation, and the liturgy absorbed them: penitential poems naming the dead entered the memorial prayers, and Ashkenazi practice acquired a layer of remembrance built specifically on 1096.
What is left on the ground is unusually complete for medieval Jewish Europe. The cemetery at Worms has been in use since the eleventh century, the ritual baths at Speyer and Worms survive as built structures, and the synagogue precincts can still be walked. The three cities' medieval Jewish quarters were added together to the UNESCO World Heritage list in 2021.