To fortify a place means to make it stronger and more difficult to attack, often by building a wall or ditch round it. British soldiers working to fortify an airbase in Bahrain
If food or drink is fortified, another substance is added to it to make it healthier or stronger. It has also been fortified with vitamin C fortified cereal products
To strengthen and secure by forts or batteries, or by surrounding with a wall or ditch or other military works; to render defensible against an attack by hostile forces