The Egyptian pyramids have stood for millennia, but they could have been stronger.
Source: KennyOMG via Wikimedia
Yes, even after enduring 5,000 years of sandstorms and erosion the Pyramids at Giza still stand tall and proud… but they could have been built even better. Instead of four sides, Egyptian engineers could have used a tetrahedron--a three-sided pyramid on a triangular base.
The stability of a tetrahedron would have made the pyramids even more durable… and maybe even useful. Think of the metrology applications of using that solid structure as a base!