An Etymological Dictionary of the German Language/März
März, m., from the equiv. MidHG. męrze, m., OHG. męrzo, marzeo, m., ‘March,’ from Lat. (mensem) Martium. The corresponding Westphal. märte, MidLG. męrte, as well as Du. maart, make it probable that März was borrowed previous to the OHG. permutation of consonants about the era of the Merovings, and in fact contemporaneously with August, Jänner, and Mai. E. March, Mid. marche, was borrowed at a some what later period from OIr. march (ModFr. mars).