I'd say Philadelphia, the symbolsim of having the Capital where the First Continental Congress was held and the Declaration of Independance signed would be very impressive. How about an insciption on a new monument in the center of the city: This city of Philadelphia, shining capital of these United states of America, was chosen for her full hearted embrace of the revolutionary Ideals and democratic principles as expounded by our founding fathers, to be seat of this great nation's government.
The Mall analogy could be constructed leading south at right angles to the city center, perhaps along the line of Broad Street?