San Margherita Lines are a line of bastion fortifications built, by the Knights of St John, around Cospicua in Malta to protect the harbours of Birgu and Senglea. By about 1645 the main bastions had been built but the walls were not complete. Nevertheless in 1670 work started on a new line of defence, the Cottonera Lines, which lay outside the San Margherita Lines. Work also stopped on the Cottonera Lines with the work on that line also not completed.
In 1715 work re-commenced on both the Cottonera and San Margerita Lines, and they were both completed by 1736.
When complete the San Margerita Lines had five bastions, two demi-bastions, six curtain walls, three main gateways, two sally ports, covered way and lunette and glacis.
In the 1850 the British made major modifications to the Santa Margherita Lines with the building of Fort Verdala Barracks, The British also built built St Clements Retrenchment linking the Santa Margherita Lines with the Cottonera Lines.
The Western end of the Santa Margherita Lines, around St John Almoner Bastion, was also partly demolished in about 1900 with an expansion of the Dockyard area.