A small Portuguese city has been declared a new UNESCO World Heritage Site, bringing the total in the country to 13.

The garrison border town of Elvas and its fortifications were added by the World Heritage Committee due to it being an “outstanding example of a garrison town and its dry-ditched bulwarked defence system, which developed in response to disruptions in the balance of power within 17th century Europe”.

As one of the greatest and most heavily fortified frontier towns in Europe, Elvas contains remains dating back to the 10th century ad and its fortification began when Portugal regained independence in 1640.

The fortifications designed by Dutch Jesuit padre Cosmander represent the best surviving example of the Dutch school of fortifications anywhere.

Elvas, which has a population of around 18,000, also contains the Amoreira aqueduct which was built to enable the stronghold to withstand lengthy sieges.

With its 843 arches, the aqueduct was begun in 1498 and is one of the most impressive of its kind in southern Europe.

Elvas joins 12 other UNESCO World Heritage sites in Portugal making it a top destination for cultural tourism.

The other sites are: Central Zone of the Town of Angra do Heroismo in the Azores; Convent of Christ in Tomar; Monastery of Batalha; Monastery of the Hieronymites and Tower of Belém in Lisbon; Historic Centre of Évora; Monastery of Alcobaça; Cultural Landscape of Sintra; Historic Centre of Oporto; Prehistoric Rock Art Sites in the Côa Valley and Siega Verde; Laurisilva of Madeira; Alto Douro Wine Region; Historic Centre of Guimarães; and, Landscape of the Pico Island Vineyard Culture.

Elvas is one of 26 new sites across the world added by the World Heritage Committee during its 36th session.

The new additions include five natural destinations, twenty cultural destinations and one under the mixed category.