A $400 million mega mansion in Bel Air, California, is set to become the first residential property in American history to reach the $400m mark. The property, purchased for $35 million in 2010 by a group with ties to Qatar's ruling Al-Thani family, features roughly 70,000 square feet of living space, multiple acres of landscaped grounds, and amenities that read more like a five-star resort than someone's actual house. The estate took 10 years to complete and is estimated to be worth around $75 million. Developers and listing agents are hoping for a buyer willing to pay nine figures for the ultimate trophy asset in the world's most glamorous city.