St. Michael Demi-Bastion is a large bulwark which anchored Valletta's enceinte on the Marsamxett Harbour. The bastion was largely carved out of the bedrock forming the main land front ditch and was one of the first bulwarks to be completed after the initiation of the construction of the fortified city in 1566. The bastion contains a low piazza bassa in its left flank, protected by a massive rounded orillion believed to have been grafted onto the shoulder of the bastion around 1582. A sally-port opening in the face of the bastion provided a means of communication, via an arched bridge, to the tiered counterguard built to protect the bastion in 1640. A second but smaller bridge, likewise accessed via a rock-hewn gallery, joins the flank (or wing) of St. Michael Bastion to St. Andrew Tenaille.
The bastion had a heavily consumed masonry fabric and fissured bedrock, requiring various types of interventions to repair the damaged stonework and to remove the rampart spread of vegetation. The restoration task was made more difficult owing to the extreme height of the bastion walls which exceeded 50m along the Marsamxett side of the enceinte. The terrace platform of the bastion is occupied by Hastings Garden.