By the Main Guard, which occupies a guardhouse distant about a stone’s throw from the Constable’s quarters, the Keys are provided with an armed escort on the occasions on which they venture into the open air. This guard is ‘mounted’ daily by some thirty soldiers; they are furnished by a regiment stationed in the adjacent barracks, which were constructed to replace other buildings totally destroyed by the great fire that made such havoc in the Tower nearly half a century ago. Over and above attending to the royal Keys, the members of the guard have other and perhaps equally responsible duties to perform, being in a general way answerable for the security of the fortress and its contents during the twenty-four hours they continue ‘on guard.’ One very important item in their tour of duty may here be mentioned—this is the protection of the Jewel House, within which are kept articles of almost fabulous value, including the regalia and the remarkable Kohinoor diamond. So low in the ceiling is the entrance to this Eldorado, that soldiers of short stature are selected to stand as sentries therein; for a tall man bearing arms would, under the circumstances, be apt to excite the ridicule rather than the awe of the visitors who are conducted into the place by the Beefeaters. The Main Guard, as its title implies, is the principal one; but two other distinct guards are maintained in the Tower; and it is necessary, in order to understand what follows, to rapidly glance at these. One of them mounts at the drawbridge—a structure that no longer exists, and of which, indeed, the guard itself seems to be the sole memento. The party is what is termed a ‘corporal’s’ guard. The other, known as the Spur Guard, occupies a group of buildings which probably represent the ancient barbican of the stronghold. It is a ‘sergeant’s’ guard, and is intrusted with the keeping of the two outer gates, to which we shall have to refer later on.