moat

A moat is a deep, wide ditch surrounding a castle, fortress, or town wall, typically filled with water or designed as a dry trench. Its primary purpose is defense: a moat hinders infantry, siege engines, and mining attempts, while the surrounding ramparts and gatehouse provide protection for defenders.

Water-filled moats create a physical barrier that slows or prevents assault, while dry moats rely on depth, width, and slope to impede climbers and equipment. Moats are usually integrated with other defensive works, such as curtain walls, battlements, and drawbridges. Some moats have sluice gates or drain systems to regulate water level and prevent flooding or stagnation.

Historically, moats were common in medieval Europe and in parts of Asia and the Middle East. Their effectiveness varied with technology and tactics; with the advent of gunpowder artillery, they gradually declined as primary defenses. In many places, moats were later filled in or repurposed, but numerous examples survive as historic structures or landscaped features in parks and castle complexes.

Beyond architecture, the term moat is used metaphorically in business and economics to describe a sustainable competitive advantage that protects a company from rivals, such as strong brands, network effects, or cost leadership.