Here are examples of the word/phrase "fortifying" used in a sentence and paraphrased in a sentence...
The enemy is fortifying their defenses with barricades.
The enemy is strengthening their defenses with barricades.
After fortifying the legs of the chair it was okay to sit on.
After reinforcing the legs of the chair it was okay to sit on.
He is fortifying is swings by using a metal bat instead of a wooden one.
He is strengthening is swings by using a metal bat instead of a wooden one.
Other Examples...