Saint Magnus-the-Martyr dates from the early twelfth century.
Saint Magnus was the first church to be destroyed in The Great Fire as it is only 300 metres from the source of the fire in Pudding Lane.
The church was rebuilt by Wren in 1676 only to be partially destroyed by another fire in 1760. At that time London Bridge was being widened and so the western part of the church was not rebuilt.
Saint Magnus only received minor damage during The Second World War.
More information can be found on Wikipedia and from Saint Magnus' website.