The actual clearing of Pennsylvania Avenue did not begin until spring 1796. Much of Pennsylvania Avenue below 9th Street was swampy and nearly unusable, as Tiber Creek curved north to border the avenue at 9th Street and again at 5th and 4th Streets before actually crossing it at 2nd Street. The damp earned the street the nickname of the "Great Serbonian Bog." (This marshy area was filled in and dried beginning in 1816.) In the fall of 1800, Pennsylvania Avenue was cleared of underbrush, and a raised footpath covered in stone chips was built. A stone bridge over Tiber Creek at 2nd Street was also built during this time, being replaced by a brick arch in 1817. On March 3, 1803, President Thomas Jefferson ordered that Pennsylvania Avenue be widened and the road completed. Benjamin Henry Latrobe, the architect newly hired to supervise the avenue's reconstruction, built three lanes separated by four rows of Black Poplars.