Actually, I don’t quite feel good about a cylinder having a square cross section.
Consider a square in front of you with its edges horizontal and vertical. (Say, drawn on your monitor.) Then consider the line running from the top of the square to the bottom of the square that passes through the center of the square. What happens when you rotate the square around that line?
Consider a square in front of you with its edges horizontal and vertical. (Say, drawn on your monitor.) Then consider the line running from the top of the square to the bottom of the square that passes through the center of the square. What happens when you rotate the square around that line?