In the days of the Old Testament, battles were won and lost on the ground. There were no airplanes or missiles. If you wanted to protect something you put it behind a thick wall and up high. Using these principles of protection, a big tower was the best form of protection. From the top of the tower you have good vision and are able to defend. It would have been very difficult for a foot soldier to get in and up the tower.
Proverbs 18:10 uses a tower as an analogy:
The name of the Lord is a strong tower; the righteous run to it and are protected.
God is the best protection, and those who turn to Him are protected. Even though times may be tough, His promise to take care of us remains. Who do you turn to for protection?