The last time the National Mall nearly ran out of space, planners and historians literally created more room for the nation’s monuments out of thin air — or rather, land. In 1902, the McMillan Commission, led by then-Sen. James McMillan of Michigan, was charged with expanding the National Mall, guided by Pierre L’Enfant’s original vision for the city. With the Washington Monument as the center axis, the commission envisioned extending the west end of the Mall to the Potomac River for a memorial honoring President Lincoln.

Meanwhile, the Tidal Basin was reshaped and land filled in to create a southern view of the Washington Monument where the Jefferson Memorial now sits.