Complex sentence: Because of this desire, they hired the same architect who originally had built the "Rennverein", Otto Marc arch decided to bury the stadium in the ground ("Erdstadion", in German).
Split into simpler sentences: Because of this desire, they hired the same architect who originally had built the "Rennverein", Otto March. March decided to bury the stadium in the ground ("Erdstadion", in German).