The immediate London basin resembles London's present county: the three most southerly boroughs reach into the North Downs broad escarpment; those opposing take as their northern edge a broken ridge, low in the north-east, high in the north-west, along which is the Grim's Ditch earthwork.

The two highest ridges in Greater London run along its southern edge (bordering Westerham, Kent and Woodmansterne, Surrey).

Later, it was the country home of W. S. Gilbert (of Savoy opera fame) – he suffered a heart attack and drowned while trying to save a swimmer in the lake in the grounds.

[3] There is another earthwork close by in Pear Wood, Brockley Hill that has been suggested as an eastern continuation of the Grim's Dyke.

This monument is of Roman or post-Roman date[4] and runs at ninety degrees to Watling Street.51°37′21″N 0°21′27″W / 51.62252°N 0.35751°W / 51.62252; -0.35751 The earthwork gave its name to the telephone exchange for Stanmore.