Mark O’Brien (Halt and Catch Fire) has been cast as a series regular opposite Aldis Hodge and Kevin Bacon in Showtime's drama pilot City on a Hill, executive produced by Ben Affleck and Matt Damon. Michael Cuesta (Homeland, American Assassin) is directing and executive producing. Written by Chuck MacLean (Boston Strangler) based on an original idea by Affleck and MacLean, City on a Hill is set in Boston in the early '90s when the city was rife with violent criminals…