The fortifications of Australia were built primarily during the 19th and early 20th centuries to protect against potential invasions. Key sites include the Sydney Harbour Fortifications, which feature Fort Denison and Middle Head, and the Port Phillip Heads Fortifications near Melbourne. These structures were designed to defend against naval attacks and reflect the military architecture of their time. In addition to coastal defenses, Australia also constructed inland fortifications, such as Fort Scratchley in Newcastle and Fort Lytton in Brisbane. Many of these sites are now preserved as historical landmarks, offering insights into Australia's military history and the strategic concerns of the era.