The Port Phillip Heads Fortifications are a series of coastal defense structures located at the entrance of Port Phillip Bay in Victoria, Australia. Built in the 19th century, these fortifications were designed to protect the growing city of Melbourne from potential naval threats. Key components include the Fort Nepean, Fort Queenscliff, and various gun emplacements. These fortifications played a significant role during both World Wars, serving as military installations. Today, they are part of the Port Phillip Heads Marine National Park and are recognized for their historical significance, attracting visitors interested in Australia's military heritage and coastal history.