On Grand Parade.
The plaque, set on a block of granite, stands beside a full-size layout of the Guardroom site which has each of the original walls represented by a line of bricks.

The Guardroom Plaque
Site of the Garrison Guardroom

The main Guard House of Portsmouth Garrison was built during the reign of George I 1714-27. From here sentries were posted to their various duties. The centre of military activity within portsmouth, this area was the setting for important ceremonial occasions. The building was demolished in 1883 at the time of the demolition of the town's fortifications.
The works which define the stucture of the Guard House, were undertaken in 1985-6 by Portsmouth City Council on behalf of Hampshire County Council.

Further Information

The brick lines embedded in the ground represent the walls of the Guard House as they appeared before about 1860. At some time after that date a row of cells were constructed at the rear of the building and these do not appear on the ground plan.
Further information about the Guard House and a 3D model of it can be seen at our sister site History InPortsmouth.