When
prisoners were brought to the Tower, and most particularly
high-ranking prisoners of state, they were led into the
Tower from the Thames via Traitor's Gate (presumably because
that was the more secure way to incarcerate people who
may well have armed bands of men waiting in the streets
to rescue them).
Over
the years Traitor's Gate has assumed an aura of hopelessness,
as so few of the people brought in via this Gate ever
left the Tower alive.
In
the image above Traitor's Gate is at the head of the steps
to the left of the picture.