The city of Xanten and its Dom.
Offices for Victor are in the antiphoner D-X H 104, fols 314v-318v, under the rubric De sancto victore martire et sociis suis (basically the same office as the one in NL-Uu 406 for Gereon and companions), with the incipit of the hymn Rex sempiterne lucis auctor.
This office is followed by another one (fols 319v-322r; rubric: alia) starting with the Vespers antiphon O quam preciosa mors sanctorum, o quam digne; Matins antiphon Sub Maximiano qui impietatem.
Chants for his octave are on fols 325r-326r.
A sequentia O beata beatorum martyrum solemnia is in the NL-Uu 417 (Utrecht Prosarium).
A strange ceremony for the 'deportatio s. Victoris' is described in D-Mbsb Clm 28546 from the Xanten Dom.