Southsea Common, pictured circa 1900.
Strictly speaking, the Common was owned by the military up until 1922, when Portsmouth Corporation purchased the land from the War Department. Although the general public was permitted access to most areas of the Common prior to this date, from time to time some areas would be placed out of bounds, if required for military use.
The open space was frequently used for musters and parades, which were a popular spectacle in Victorian times, as can be seen from the picture below, which depicts the Navy Festival of 1865.