Yes, "marha" can well be a Germanic element, living on in the English word "mare" and the German "Mähre" (nowadays a word for an old, bad horse; up to the 16th cent. it just meant "mare", later "horse" in general, and towards the end of the 17th cent. took the above meaning) and "Marschall". It is likely to be of Indoeuropean origin, but also may be loan word from Celtic.
(This is taken from: dtv Etymologisches Wörterbuch des Deutschen, München 1993)