'Tower' in the Bible

Or those eighteen, upon whom the tower in Siloam fell, and slew them, think ye that they were sinners above all men that dwelt in Jerusalem?

For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it?

Otherwise, when he has laid a foundation and is not able to finish the tower, all who see it will begin to make fun of him.