Boston's best-known park is the 19-hectare (48-acre) Boston Common, located in the heart of the city, along with the 10-hectare (24-acre) Public Garden. The land for the Common was purchased by the city in 1634 from a property owner for $150. Today's visitors to the Common jog, skate, or play frisbee on a historic site that has, in its time, served as a pasture, execution and drill ground, and football field. Also within the city limits, located in the Back Bay, are the Back Bay Fens, which extend from Beacon Street to Brookline Avenue, and the Esplanade along the Charles River, site of the summer Boston Pops concerts, which take place in the Hatch Shell. Other notable parks in the Boston area include Harvard's 90-hectare (223-acre) Arnold Arboretum and Franklin Park and Zoological Garden, covering 213 hectares (527 acres).