From the smithsonianmag.com article:
Today’s Washington, D.C. owes much of its unique design to Pierre Charles L’Enfant, who came to America from France to fight in the Revolutionary War and rose from obscurity to become a trusted city planner for George Washington. L’Enfant designed the city from scratch, envisioning a grand capital of wide avenues, public squares and inspiring buildings in what was then a district of hills, forests, marshes and plantations.
Read the full article here. There is also a video to watch at the smae link.
Also don’t miss this informative interactive map, it allows you to fly around a pixel Washington D.C. and learn about the various sites. Click on any of the buildings for a breif summary.