For almost 40 years, Continental operated a very large hub in Denver, Colorado, but took the decision to close that hub in 1995 immediately after the opening of Denver International Airport (DIA), which represented a significantly higher-cost operation than the former Stapleton Airport, which DIA had replaced. The abrupt nature of this change came as a shock to Denver, which was experiencing dramatic growth. The void left by Continental's departure allowed the establishment of the "new" Frontier Airlines (a startup, rather than the original carrier of that name). Both Frontier and Southwest Airlines (which entered the Denver market after Continental's dehubbing) expanded quickly to fill the vacuum created by Continental's closing of its Denver hub.