Protected from the wind by the surrounding hills, Mondorf benefits from a pleasant climate, and people settled here very early on. Its first inhabitants were the Celts. The Roman presence began in 65 BC and the Castel, built on Celtic fortifications and intended to protect the Lyon-Coblenz road, dates from that era. It was the Franks who gave Mondorf its name. Charlemagne had a niece called "Muomina" who donated all her possessions to Echternach Abbey. Amongst them was a small village which thus took the name of "Muomendorph". Charlemagne married Hildegarde de Thionville. Because this meant making numerous trips between Thionville and its capital, Aix-la-Chapelle, he had a residence built at Mondorf (Pfalz) which served as a half-way house.
Situated at the crossroads between Germany and France, Mondorf has always been a place of battles, which caused great suffering. The village was pillaged and burnt down many times. Saint-Michel church, built in 1065, was destroyed and rebuilt four times, the last time in 1764-1766 by a priest with the curious name of "Ungeschik" (clumsiness) who benefited in doing so from the help of the Abbott of Echternach. Its furnishings and paintings today attract many visitors.