Venice, the leaning tower of Pisa, and Charlotte's light rail

My pastor's wife, Beth, just called and we had the ensuing conversation:

Brad: "Hello?"
Beth: "Brad! I'm so glad you answered!"
Brad: "Well, I'm glad you called!"
(Laughter because of my great wit and outstanding timing)
Beth: "I have a question for you..."
Brad: "Okay..."
Beth: "Why did they build Venice on water?"

I'm praying for her...