Throughout the centuries, Spain has been the stage of many clashes between civilizations, with the constant battling between Iberians, Celts, Romans, Goths, Visigoths, Jews and Muslims leading to many cities being born as fortified strongholds.
Just more than 100km from Madrid in the arid Spanish plains, Ávila is generally shunned in favour of nearby Segovia for day trips from the Spanish capital. But its 2,500m of city walls -- one of the best preserved examples of medieval architecture in Europe -- are well worth the detour. Although some historians suggest the birth of the walls goes back to the original Roman settlements, the first recorded mention dates from the late 11th Century, when King Alfonso VI of Castile ordered the fortification of the city, a task completed in an astonishing nine years. The walls were declared a Unesco World Heritage Site in 1985. (Ken Welsh/Getty Images)