The domed US Capitol Building is recognized around the world as America's most iconic symbol, the forum for representative democracy, and the physical stage for the transfer of executive power. As the United States grew in size and complexity, the Capitol was built, rebuilt, enlarged, and extended many times under the direction of the few who have served as Architect of the Capitol. This official heads the agency dedicated to preserving and upgrading this magnificent structure, and all the buildings and grounds of Capitol Hill.

In Under the Dome, Alan Hantman, the Architect of the Capitol from 1997 to 2007, provides a personal account of how the Capitol works as a physical space; who runs it, how and why decisions are made about the security of the Capitol and the people who work there, and how politicians think about the Capitol Building. He also recounts security threats to the Capitol during his tenure—including the 1998 shooting murder of two police officers and the Capitol evacuation on 9/11 as a hijacked airplane approached—that underscore one of his greatest challenges as Architect. The tension between securing the Capitol and opening it to the public drove the design and construction under his direction of the Capitol Visitor Center, the largest expansion of the Capitol in its history, increasing its size by seventy percent.