In this talk I responded to an inquiry as to how the present-day forms of the place name 'Trier' entered into the West Slavic languages (pol. Trewir, tsch., slk.
Trevír), whether by German(ic) mediation or via borrowing from medieval Latin. First, the history of the Latin name and its phonetic structure was discussed, then its adoption into pre-High German together with its further development in the German vernacular.
Subsequently, the present situation in the Slavic languages was presented and historically relativized on the basis of older evidence. For Czech and Polish, more extensive research of the sources was conducted and the resulting series of attestations evaluated here.
Against this background it can be stated that the West Slavic forms cannot be traced back to an early borrowing from the German vernacular. Rather, it must be assumed that they were adopted on the basis of Latin texts.
This can be traced well in Czech, where at first the later vernacular German form (Trier) was adopted into colloquial speech and, with the emergence of Czech writing, was then also used in written language. Only later, beginning under the influence of the chronicle of Václav Hájek z Libočan and possibly supported by its use in neighboring Poland, was a Latin-based form gradually adopted into Czech - initially in the written language and consequently also in the vernacular.