A rampart is a thick defensive wall built around a castle, fort, or city to protect it from attackers. Picture a massive wall of stone or packed earth, often wide enough on top for soldiers to walk along and defend their position. Medieval castles had ramparts where archers could stand and fire arrows down at enemies below.

Throughout history, cities under threat built ramparts to keep invaders out. The famous walls of ancient Constantinople had enormous ramparts that helped protect the city for over a thousand years. Fort McHenry in Baltimore has ramparts that Francis Scott Key wrote about in “The Star-Spangled Banner” when he described seeing the American flag still flying after a British attack.

You might hear rampart used figuratively too. When someone builds a rampart against criticism, they're creating a strong defense for their ideas or position. A town might create a rampart of sandbags to hold back floodwaters. In these cases, rampart means any strong protective barrier, whether physical or not.