The challenge proved addictive , and he has been with Christo and his spouse , Jeanne-Claude , ever since , first as a consultant for '' Wrapped Reichstag '' in Berlin -LRB- 10 miles of blue rope was used to wrap the building in silver fabric -RRB- , next as the design engineer in 1996 for the as-yet-unrealized '' Over the River '' installation on 40 miles of the Arkansas River in Colorado .