Ruins are the remains of a civilization's architecture. The term refers to formerly intact structures that have fallen into a state of partial or total disrepair over time due to a variety of factors, such as lack of maintenance, deliberate destruction by humans, or uncontrollable destruction by natural phenomena. The most common root causes that yield ruins in their wake are natural disasters, armed conflict, and population decline, with many structures becoming progressively derelict over time due to long-term weathering and scavenging.