The road called 'Frognal
' follows the route of one of main branches of the River Westbourne
- this branch being called the 'Kilbourne'.
Downstream it will flow through Kilburn, Bayswater and Knightsbridge - giving each of those places, indirectly, their names.
But up here in the hills of Hampstead, the infant river flows beneath modern residents of 19th century houses.
Below the house with the address of 16 Frognal
, the lay the junction where the main Kilbourne stream, flowing downhill beside Frognal
, met a smaller tributary which began in a boggy area beneath the future Netherhall Gardens
This can be seen on the 1870 map where the marker shows the spot.
Further along its course, the Kilbourne will meet the Cannon Stream flowing down from Whitestone Pond
and, combined, form the Westbourne.