No, the Lincoln Memorial has not been there forever

That's the Parthenon in Greece you're thinking of!

The Parthenon is almost 2500 years old, designed by Pericles

Built on the Acropolis in Athens, it was a lavish temple to Athena, the goddess associated with warfare, protection, power, and wealth. An enormous golden statue of Athena dominated the temple. Over a thousand years later, the temple was a Christian Church dedicated to Mary, and later yet, it became a mosque.

Lincoln's Memorial, dedicated in 1922, just turned 100

Fifty-seven years passed after Lincoln's assassination before the Memorial was funded, agreed upon, and built on the western part of the Mall that didn't even exist when Lincoln was alive. Designed by Henry Bacon in the heyday of neo-classicalism in this country, it was part of the City Beautiful movement. A time when imitating ancient Greek and Roman architecture was the style favored to connote democratic ideals and civic order.

When I first saw it over 50 years ago, I didn't think to question its origins - so linked was it in my mind to images of Greece, it seemed like it must have been there forever. 

See those steps on the Potomac River side

They're called the Watergate Steps  (the source of name of the nearby Watergate complex where the infamous break-in occurred.)

These 40 steps were designed to be the place where VIPS might be received as they sailed up the Potomac to the Capital.  That never occurred, but for years, something more democratic did.

The Watergate Steps became a concert place

The orchestra played on a barge docked in the Potomac while the audience sat on the steps beneath the night sky. (You can see it in the 1958 Cary Grant and Sophia Loren movie, Houseboat.) The “Sunset Symphonies” lasted from 1935 until 1965, when they were canceled because of jet noise. How unfortunate!

Today they are a useless set of stairs with a busy road curving beneath them. Occasionally bikers rest there.