The pre-history of the islands is subject to the inherent problems of their isolation. However, the appearance of worked tools allows us to assume that man has inhabited the islands since these times. Man's presence in the Palaeolithic period can not be ascertained as the sites which have been found are not coastal ones. Whatever the conclusion, it is true that many Stone Age tools have been found although it is difficult to date them accurately.
At the end of the Bronze Age came a new population, the development of which lead to the most characteristic culture of the North-West of the Iberian peninsular - the Castros. They built settlements on high grounds and hills with fortifications to protect their huts. They had polished stone tools and rudimentary, thick ceramics. Along the pathway that leads to the ruins of the island's old monastery, you can find many fragments of ceramics from this period.
As an example of the Castro culture of the islands, you can visit the settlement of "As Hortas". This stretches across the incline between the small Faro do Principe Lighthouse and the main lighthouse.
In 138 BC, the Gallaecia tribes fought the Roman army. Around 90BC, Publius Crassus undertook an expedition to Galicia to search for the Tin Islands (The Cassiterides) and in 60BC, Julius Caesar started his war campaign which forced the indigenous Lusitanians to flee from Mount Herminio. The Herminians abandoned the high grounds between the Duero and Miño rivers and headed toward Galicia, arriving in Baiona and sailing across to the islands. On his arrival, and seeing how close the islands were to the mainland, Caesar ordered boats to be built to attack the islands. Once the fleet set sail they were faced by the steep cliffs on the south of the islands and had to land on Rodas Beach where, after a bloody battle, they defeated the Herminians. Many more battles lay ahead before the Romans finally conquered the whole of the NW peninsular.
Although it is known that the Sueves sailed these waters, there are no remains from this time. In the 6th century AD, the time of a proliferation of religious orders of the Middle Ages, two convent-hermitages were founded on the island: San Martiño on the south island and San Estevo on the north island. The Interpretation Centre is built on the ruins of San Estevo where some of the anthropomorphous burial chambers can still be seen.
Despite attacks by the Normans, religious communities prospered and rule the population as a feudality. In the mid 16th century, the population started to abandon the islands due to attacks by the Turks, Tunisians and the English. Francis Drake attacked the Ría de Vigo and sacked the islands.
As a result, the archipelago was fortified in the 19th century and an arsenal was established in the old San Estevo monastery and a military base and prison were built near to Nosa Señora beach. With this increased level of security, the islands started to be re-populated and new industries sprung up. Around 1840, two salt plants were built - one on the site where the restaurant now stands and one on the south of the island. The lighthouse Faro de Cíes was also built in this era (1852). A tavern was also built on the banks of the lagoon which was also used as a lobster farm. Competition from the mainland led to the decline of the salt industry and by 1900 the factories were only used as storage areas.
A small population remained on the islands, the majority from Cangas, but this slowly decreased until the mid 20th century. At the same time, the wealthy classes started to come to the islands for their holidays and, in the 1950s large-scale tourism arrived. This led to the need to protect the natural beauty of the islands and they were declared a National Park in 1980.