An Etymological Dictionary of the German Language/Mauer
Mauer, f., from the equiv. MidHG. mûre, mûr, s., ‘wall,’ OHG. mûra, f. (mûri, f.), ‘wall,’ from Lat. mûrus, with an abnormal change of gender, which is probably caused by an OTeut. word for ‘wall’; comp. Goth. waddjus, f. At the same period, before the HG. permutation, OSax. mûr, AS. mûr, m. (OIr. múr), were also borrowed from the Lat., like other words relating to stone buildings; comp. Siegel, Fenster, Pforte, Speicher, &c.