He is a working dog and he is bored. My guess is he might have developed an obsessive behavior out of boredom due to lack of attention he received from previous owner. Seek out a trainer who can assist you in modifying his circling. Find an outlet for his energy. Give him a job. Maybe agility, maybe fly-ball, if his temperament is solid enough maybe schutzhund. He is beautiful and is worth the work. Congrat on your beautiful boy!
Athena- Long Coat GSD -CGC
Sinister Black- GSD