The historical,
ancient city of London until after medieval times was
the area within the
city walls: basically the area that the Romans
colonised and called
Londinium, although there was a small
Royal/Church presence at
Westminster about 3-4 miles westwards along
the
river from there. As a side note, the area of London
that originally fell within the city walls is now the
financial district
and is still called "
The City".
Once London finally started growing too large to be contained within
the ancient walls, a natural development was to follow the river towards
the great abbey at Westminster and the royal courts there. Being west
of the City this region gradually became known as the West End, the
East End for a long time being a run-down residential area of slums,
sweatshops and the dockyards, although it is considerably improved
these days.
Today's modern West End isn't a precisely-defined region within London.
It certainly encompasses the theatre district of Soho and nearby
Chinatown, but it also includes shopping areas such as Oxford Street,
Regent Street and Carnaby Street. Many people would also include the
Royal Parks and Buckingham Palace as part of the West End, although
others wouldn't. Like I said, it's a fairly loose definition, generally
meaning "that part of central London which isn't
the City".