Landscape with Ruins. Ruins are the remains of human-made architecture: structures that were once intact have fallen, as time went by, into a state of partial or total disrepair, due to lack of maintenance or deliberate acts of destruction. Natural disaster, war and population decline are the most common 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, ancient universities, 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, Stalingrad, Konigsberg, 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. Entire cities have also been ruined, and some occasionally lost completely, to natural disasters. The ancient city of Pompeii was completely lost during a volcanic eruption in the 1st century AD, 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 Campagna 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 monasteries fell into ruin when their assets, including lead roofs, were stripped. In the 20th century, 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 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. Post-colonial Ireland has encouraged the ruin of grand Georgian houses, symbols of British imperialism. As a rule, towers built of steel are dismantled, when not used any more, because their construction can be either rebuilt on a new site or if the state of construction does not allow a direct reuse, the metal can be recycled economically. However, sometimes tower basements remain, because their removal can sometimes be expensive. One example of such a basement is the basement of the former radio mast of Deutschlandsender Herzberg/Elster. The basements of large wooden towers such as Transmitter Ismaning may also be left behind, because removing them would be difficult. The contemplation of rust belt post-industrial ruins is in its infancy. In the Middle Ages Roman ruins were inconvenient impediments to modern life, quarries for pre-shaped blocks for building projects, or marble to be burnt for agricultural lime, and subjects for satisfying commentaries on the triumph of Christianity and the general sense of the world's decay, in what was assumed to be its last age, before the Second Coming.