The document discusses the evolution of shelters from early prehistoric times to modern periods. It describes how early humans initially took shelter in trees and caves for protection, before beginning to construct more rudimentary shelters using stones, wood and other natural materials. Over time, shelters incorporated new building materials like clay bricks and glass, and architectural styles advanced with developments in building techniques during historical periods such as the Stone Age, Early Modern Period and contemporary styles of kachcha, semi-pukka and pakka construction. The document traces the progression of shelter design and materials in tandem with human technological and societal development.