George Whitefield used to preach here in the open-air to crowds of upto 20,000. It was said their singing could be heard 2 miles off, and his voice 1 mile! After hs death, one of his friends planted it with fir trees. It is still named after Whitefield today, even on hte official boards.
Wednesdy May 16th, 1739, Journal of Charles Wesley: "I attended G. Whitefield to Blackheath. He preached the rain to many listening sinners. At Fetter-lane a arose about lay-preaching. Many, particularly Bray and Fish, were very zealous for it. Mr. Whitefield and I declared against it."
John Wesley's first field-preaching in London was here in June 1739. http://edithsstreets.blogspot.co.uk/2010/03/tq-388-764-thames-tributary.html