You will find St Michael’s Gate at the very top of Charles V Wall. (See LINK) It was presumably given the name of St Michael’s because anyone wanting to visit the cave of the same name would have had to walk through the gate to get to it. At least that is what you would do if you started off from the Signal Station. Once through the gate you simply travelled south following the track along a ridge known as Mount Misery which lead you to the entrance of St Michael’s Cave.
The Rock looking south more or less from the Signal Station - On the far side of a dangerous looking St Michael’s Gate two people seem to be walking along the track to or from St Michael’s Cave (Edmund Gilling Hallewell)
Another view of St Michael’s Gate this time from an upper footpath looking north - The lower footpath shown on the left in the engraving led to St Michael’s Cave (T.M. Baynes from H. A. West) (See LINK)
This late 19th century photograph of the Gate suggests that it was not originally part of the 16th century Charles V Wall but perhaps a later addition added on by either the Spaniards or the English (c1870 - James H. Mann - Crop) (See LINK)
Throughout the 16th to the very early 18th century St Michael’s Cave was known in Spanish Gibraltar as la Cueva de San Miguel. According to the Gibraltarian historian Alonso Hernández del Portillo (see LINK) writing in the early 17th century:
. . . hay otra que se dice la cueva de San Miquel, que de debió de poner este nombre por parecerse a la del monte Gargano de la Pulla, donde se apareció el Arcángel San Miquel . . .
(1796 - The Rev. Cooper Willyams) (See LINK)
During the early 17th century and well into the 19th the new British landlords tried hard to officially change the name to a more familiar St George’s Cave. It never caught on and St Michael it has remained ever since - none of which really helps to determine when the gate was constructed.