What if Jupiter and Saturn had traded places? The king of planets starts at Saturn's distance (~9.5 AU) while the ringed giant sits at Jupiter's (~5.2 AU) — both in their real 1 January 2025 sky positions, just with roles reversed. The real Solar System's architecture depends on these two staying separated: swap them and the balance collapses. Secular resonances, repeated close approaches, and gravitational waves from the misplaced giants batter Mercury, Venus, Earth, and Mars while Uranus and Neptune look on from the outer cold. The Nice model shows that even small changes in giant-planet orbits can reshape the entire system; swapping them is far more violent.