Mind you ..thinking about there have been lots of gates on London Bridge ....it also had a Traitors Gate at one time and a New Stone Gate during Tudor times .
There was a traitors gate on Tower Bridge at one time ..they stuck peoples heads there on poles !! But it's not as famous as the one at the tower which is more well known as it is still there.I think it probably disappeared when London Bridge burnt down during the great fire so it's a bit obscure.