Pennsylvania Avenue from the U.S. Capitol to the Treasury Building beside the White House, is Washington's Main Street, the inaugural avenue of our presidents, our Champs Elysees.

Since cameras were invented, one of the favorite spots for photographers has been from behind the iron railing fence of the 1836 Treasury Building, looking east on Pennsylvania Avenue from 15th Street NW.

The Treasury Department, the first federal department building is where it is -- blocking the White House-Capitol vista envisioned by Pierre L'Enfant when he laid out the city in 1791 -- because President Andrew Jackson put his cane on the spot and reportedly said "Right here is where I want the cornerstone." Before him, George Washington had predicted the avenue, then a muddy, rutted road, would some day be "most magnificent and most convenient." Thomas Jefferson, the first president to have an inaugural parade up the avenue, apparently agreed and soon had four rows of Lombardy poplars planted along Pennsylvania Avenue to give it grandeur. Then in 1833 Congress paved over the dirt and mud with a macadam road.

In the early 1867 photo, top, "the street was still dominated by Federal-style row houses built around 1800," says Charles Suddarth Kelly in his new book "Washington D.C., Then and Now." A few large buildings soon graced the avenue, like the Willard Hotel, built in 1847, visible above the trees on the left and the National Republican Newspaper, with the mansard roof, on the right.

By 1927, middle photo, the Romanesque Revival Post Office (1899) had risen high above its classical federal neighbors, street cars were motorized and automobiles jammed the avenue, parking in the middle of the street and adding to the haze that made the capitol almost invisible.

Following his inaugural parade in 1961, President John F. Kennedy launched the drive to give the avenue the magnificence envisioned by our early presidents. Since then more than $1 billion in private and public funds have been spent on buildings and parks along the avenue. The old Post Office and the National Theater are restored, the Willard Hotel will reopen next year, new hotels and offices are up and more are coming. Four new parks now line the avenue, two more are on the way and, as in Jefferson's day, 400 new street trees have been planted.