In article , John Rowland
writes

http://www.johnchaple.co.uk/romanroad.htm

An interesting read, but I'm not quite convinced about the point of
intersection. Using the 1:50,000 map of East London, the line of
Watling Street from Kent seems to just touch the bank of the Thames at
Greenwich, rather than cross the river as shown on the map on John's
page. Maybe a slight deviation would have been needed, as the river
bank would have been a bit marshy, I'd imagine. Continuing on the same
straight line takes us to the Thames just south of the present
Westminster Bridge, perhaps not far from the horse ferry, after which
Horseferry Road was named.

I found it a bit harder to trace the line of Watling Street south from
Marble Arch, as the road curves somewhat in the stretch south from
Edgware leaving several possible alignments, but the most likely
projection would take it to the Thames just north of the Tate Gallery,
i.e. some way upstream from the other projection line. These two lines
do, indeed, seem to intersect pretty close to Buckingham Palace.
Perhaps there was some more curvature in this stretch of the Roman road,
but it's hard to guess how much, and therefore exactly where the river
crossing might have been. How far back does the horse ferry go back, I
wonder?

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Clive Page