The Pentagon is the headquarters of the US Department of Defense, so named because the complex, as seen from the air, resembles the five-sided geometric shape. It is located just outside of Washington D.C. in Arlington County, Virginia.
Homeworld Command that handles the defense of Earth and its interests also operated here when it was first created by President Henry Hayes. In 2009, several technology developed and acquired by SGC and Atlantis Expedition were also installed at the Pentagon. Some notable technology are the subspace communication, long-range communication device, and defense technology. Though there might be more technology installed, these are the known that had been mention in the series. (SGU: "Air, Part 1", "Air, Part 2")
- The Pentagon on Wikipedia