Map showing the earthworks and barrows:
https://www.cityoflondon.gov.uk/things-to-do/green-spaces/city-commons/farthing-downs/Documents/Farthing-downs-map.pdf
(archive link - why do they keep moving these things!)
Summary from Friends of Farthing Downs and Happy Valley
http://www.friendsoffarthingdowns.co.uk/gpage17.html
http://www.friendsoffarthingdowns.co.uk/gpage6.html
Something is not right. This message is just to keep things from messing up down the road