Ruins is a term used to describe the remains of man-made architecture: structures that were once complete but which have fallen into a state of partial or complete disrepair, due to lack of maintenance or deliberate acts of destruction. Natural disaster, war and depopulation are the commonest root causes, with many structures becoming progressively derelict over time due to long-term weathering and scavenging. There are famous ruins all over the world, from ancient sites in China, the Indus valley and Judea to Zimbabwe in Africa, ancient Greek, Egyptian and Roman sites in the Mediterranean basin, and Incan and Mayan sites in the Americas. Ruins are of great importance to historians, archaeologists and anthropologists, whether they were once individual fortifications, places of worship, houses and utility buildings, or entire villages, towns and cities. Many ruins have become UNESCO World Heritage Sites in recent years, to identify and preserve them as areas of outstanding value to humanity.
Ancient cities were often highly militarized and fortified defensive settlements. In times of war they were the central focus of armed conflict and would be sacked and ruined in defeat. Although less central to modern conflict, vast areas of 20th century cities such as Warsaw, Dresden, Coventry, London and Berlin were left in ruins following World War II, and a number of major cities around the world – such as Beirut, Kabul, Sarajevo, Grozny and Baghdad – have been partially or completely ruined in recent years as a result of more localised warfare.
Cities have been also been ruined, and some occasionally lost entirely, to natural disasters. The ancient city of Pompeii was completely lost during a volcanic eruption in the 1st century CE, its uncovered ruins now preserved as a World Heritage Site. The city of Lisbon was totally destroyed in 1755 by a massive earthquake and tsunami, and the 1906 San Francisco earthquake left the city in almost complete ruin.
Apart from acts of war, some important historic buildings have fallen victim to deliberate acts of destruction as a consequence of social, political and economic factors. The spoliation of public monuments in Rome was under way during the fourth century, when it was covered in protective legislation in the Theodosian Code and in new legislation of Majorian. and the dismantling increased once popes were free of imperial restrictions. Marble was still being burned for agricultural lime in the Roman Camapgna into the nineteenth century. In Europe, many religious buildings suffered as a result of the politics of the day. In the 16th century, the English monarch Henry VIII set about confiscating the property of monastic institutions in a campaign which became known as the Dissolution of the Monasteries. Many abbeys and monsateries fell into ruin when their assets, including lead roofs, were stripped.
Following World War II, a number of European historic buildings fell into ruin as a result of taxation policies, which required all structures with roofs to pay substantial property tax. The owners of these buildings, like Fetteresso Castle (now restored) and Slains Castle in Scotland, deliberately destroyed their roofs in protest at, and defiance of, the new taxes. Other decrees of government have had a more direct result, such as the case of Beverston Castle, in which the English parliament ordered significant destruction of the castle to prevent it being used by opposition Royalists.
The basements of large wooden towers such as Transmitter Ismaning may also be left behind, because removing them would be difficult.
Ruins remain a popular subject for painting and creative photography and are often romanticized in film and literature, providing scenic backdrops or used as metaphors for other forms of decline or decay. For example, the ruins of Dunstanburgh Castle in England inspired Turner to create several paintings; in 1989 the ruined Dunnottar Castle in Scotland was used for filming of Hamlet starring Mel Gibson and Glenn Close. Ruins are also found in many places in the online game Runescape. The Civilization series of turn-based strategy computer games features ruins as special tiles which may provide the player with a bonus when explored.