In 1876, Philadelphia played host to America's first World's Fair to celebrate the 100th anniversary of the signing of the Declaration of Independence. Officially titled the International Exhibition of Arts, Manufactures and Products of the Soil and Mine, what would be known as the Centennial Exposition hosted approximately 10 million visitors (or 20% of the US's population at the time) over the span of six months. Over 200 buildings were constructed for the event, including an observation tower, though only one was ever meant to be permanent - Horticultural Hall. Fashioned after London's famed Crystal Palace, the building survived until 1954 when it was badly damaged by Hurricane Hazel and had to be demolished. Today, four structures still remain on the grounds - the Art Gallery Building, known today as Memorial Hall and home to the Please Touch Museum; the Ohio House, which has gone through a series of various restaurants in the past 10 years; and two comfort stations, small brick buildings behind the present-day Horticultural Hall. A handful of buildings were sold off and shipped elsewhere, though only a few of them are known to still exist. An interesting list of the buildings, their histories, and their fates, can be found here.
Though it was not built until decades after the Centennial Exposition had ended, the Smith Memorial Arch now serves as a symbolic gateway into Centennial Park. The memorial arch was funded by Richard Smith, a wealthy Philadelphia industrialist who bequeathed half a million dollars in his will for the project meant to be a memorial to Pennsylvania's military and naval heroes of the Civil War. Due to unforeseen problems with sculptors and artists, the project took fifteen years to complete. The dual-columned, semi-circular structure features nine busts, three figures, and two equestrians. It was finally completed in 1912 with no fanfare or celebration, mostly due to the public having lost interest in celebrating and memorializing the Civil War.
Centennial Park & the Smith Memorial Arch