It’s not the nicest part of town (although, it is close to the trendy restaurants of Fishtown), or the prettiest park, but it worth a stop because of its importance to the history of Philadelphia. Legend has that this is the site where William Penn met with the Delaware Indians and established the “Great Treaty.” According to Voltaire, “It was the only treaty made by the settlers with the Indians that was never sworn to, and the only one that was never broken” – comparing Penn’s treaty with most others that had been made in the colonization of America.
The “treaty elm” under which the meeting took place stood until toppled by a storm in 1810. Today, a great, great, grandchild of the elm has been planted in its place. A child of the elm can be seeing growing in the gardens of Pennsylvania Hospital (A Look Inside America’s Oldest Hospital & the Oldest (Existing) Operating Theater in the World).
This c. 1800 painting by Thomas Birch (from the collections of the Pennsylvania Historical Society) shows the same view, highlighting the maritime nature of Philadelphia in that era. 
This painting by Edward Hicks, on display at the Philadelphia Museum of Art, commemorates the event.
Secrets of Philadelphia 