Maiden Castle, Dorset in the context of "Modern archaeology"

A hillfort is a type of fortified refuge or defended settlement located to exploit a rise in elevation for defensive advantage. They are typical of the late European Bronze Age and Iron Age. Some were used in the post-Roman period. The fortification usually follows the contours of a hill and consists of one or more lines of earthworks or stone ramparts, with stockades or defensive walls, and external ditches. If enemies were approaching, the inhabitants would spot them from a distance.

Prehistoric Europe saw a growing population. It has been estimated that in about 5000 BC, during the Neolithic period, between 2 million and 5 million people lived in Europe; in the Late Iron Age, Europe had an estimated population of around 15 to 30 million. Outside Greece and Italy, which were more densely populated, the vast majority of settlements in the Iron Age were small, with perhaps no more than 50 inhabitants. Hillforts were the exception, and were the home of up to 1,000 people. With the emergence of oppida in the Late Iron Age, settlements could reach as large as 10,000 inhabitants. As the population increased, so did the complexity of prehistoric societies. Around 1100 BC hillforts emerged and in the following centuries spread through Europe. They served a range of purposes and were variously tribal centres, defended places, foci of ritual activity, and places of production.

A fortification (also called a fort, fortress, fastness, or stronghold) is a military construction designed for the defense of territories in warfare, and is used to establish rule in a region during peacetime. The term is derived from Latin fortis ("strong") and facere ("to make").

From very early history to modern times, defensive walls have often been necessary for cities to survive in an ever-changing world of invasion and conquest. Some settlements in the Indus Valley Civilization were the first small cities to be fortified. In ancient Greece, large cyclopean stone walls fitted without mortar had been built in Mycenaean Greece, such as the ancient site of Mycenae. A Greek phrourion was a fortified collection of buildings used as a military garrison, and is the equivalent of the Roman castellum or fortress. These constructions mainly served the purpose of a watch tower, to guard certain roads, passes, and borders. Though smaller than a real fortress, they acted as a border guard rather than a real strongpoint to watch and maintain the border.