The "keystone" of the Thomas Jefferson Parkway is the Saunders Bridge. Opened on July 3, 2002, the bridge serves as Monticello's main vehicular entrance and a link between sections of the Saunders-Monticello Trail on the north and south side of Route 53. Both the bridge and the Saunders-Monticello Trail are named in grateful recognition of a gift from Mr. and Mrs. Thomas A. Saunders III. Mr. Saunders is a former chairman of the Thomas Jefferson Foundation's Board of Trustees.

Thomas Jefferson, himself, envisioned a bridge in the same general vicinity when he devised plans to connect his property at Monticello to land he owned across the road, known then as Montalto (now Brown's Mountain). In his "General Ideas for the Improvement of Monticello" (ca. 1804), he discussed linking the upper (Montalto) and lower (Monticello) park lands without impeding public traffic through the "thoroughfare" gap:

"The north side of Monticello below the thoroughfare roundabout quite down to the river and all Montalto above the thoroughfare to be converted into park & riding grounds, connected at the Thoroughfare by a bridge, open, under which the public road may be made to pass so as not to cut off the communication between the upper and lower park grounds."

The current necessity for a new, safer entrance to Monticello for cars, and the imperative to link the Saunders-Monticello Trail with Monticello itself suggested a return to Jefferson's vision for a bridge.

The resulting Saunders Bridge, as designed by Rieley and Associates of Charlottesville, is a massive, stone arch spanning Route 53. The elliptical arch of the bridge recalls the Pont de Neuilly, which Jefferson so admired during his stay in Paris, while the fieldstone facing evokes the architectural tradition of great parkways such as the Blue Ridge Parkway. A stone bridge is one of the signatures of American parkways.

The bridge stands twenty-one feet under the keystone (thirty-five feet to the top of the bridge), high and wide enough to accommodate two tractor-trailers, side by side. It will arch over three lanes of traffic, while carrying two lanes of traffic (plus a sidewalk connected to the Saunders-Monticello Trail) into and out of Monticello.

Workers employed ancient and seldom-used technique to build the bridge. Instead of erecting a frame, earth was packed under the span to support the arch as it was built. 3,200 tons of concrete was poured to form the footings, walls and vault, which will be faced with stone. The 32,000 square feet of fieldstone facing comes from Highland County, Virginia, while the arches are highlighted by New England granite blocks, carefully cut to maintain a precise geometric ellipse.

W. C. English Inc., of Lynchburg, Virginia, began building the bridge in 2000, and Espina Stone of Fairfax, Virginia was the masonry contractor.