To fortify a place means to make it stronger and more difficult to attack, often by building a wall or ditch round it.

If food or drink is fortified, another substance is added to it to make it healthier or stronger.

If you are fortified by something such as food, drink, or an idea, it makes you feel more cheerful, determined, or energetic.

To fortify something means to make it more powerful and more likely to succeed.