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
make strong or stronger; "This exercise will strengthen your upper body"; "strenghten the relations between the two countries"
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