The Twelve Apostles is a collection of miocene limestone rock stacks jutting from the water in Port Campbell National Park, between Princetown and Peterborough on the Great Ocean Road.
The apostles were formed by erosion: the harsh weather conditions from the Southern Ocean gradually eroded the soft limestone to form caves in the cliffs, which then became arches, which in turn collapsed; leaving rock stacks up to 45 metres high. The site was known as the Sow and Piglets until 1922 (Muttonbird Island, near Loch Ard Gorge, was the Sow, and the smaller rock stacks the Piglets after which it was renamed to The Apostles for tourism purposes. The formation eventually became known as the Twelve Apostles, despite only ever having nine stacks.
In 2002, the Port Campbell Professional Fishermens Association unsuccessfully attempted to block the creation of a proposed marine national park at the Twelve Apostles location but were satisfied with the later Victorian Government decision to not allow seismic exploration at the same site by Benaris Energy believing it would harm marine life.
The stacks are susceptible to further erosion from the waves. On 3 July 2005, a 50 metre tall stack collapsed, leaving eight remaining. On 25 September 2009, it was thought that another of the stacks fell, but this was actually one of the smaller stacks of the Three Sisters formation. The rate of erosion at the base of the limestone pillars is approximately 2 cm per year. Due to wave action eroding the cliff face existing headlands are expected to become new limestone stacks in the future.