Lewis & Short

Matrae, ārum, f. (dat. plur. MATRABVS, for Matris, Inscr. Grut. 29, 1), or Matres, more freq. Matronae, the protecting goddesses of a country, city, or place: MATRIS AVGVSTIS D. D., Inscr. Grut. 90, 1; so ib. 2 sq.