Dingding, The major reason I researched Compass is that it is the only tech willem did not have atm, in isolated or semi-ioslated, my 1st goal is almost always CS, and Optics is 2nd. To 940AD -- Astro Spoiler : Tech: Compass (trade for Alpha)->Math->Currency->CoL->CS (JC came 1 turn before CS which opened the trade opportunity, so I traded MC and Machinery)->Optics->Nat Currency in 75AD, cities and cottages start to mature. BPT is close to 200. CS in 400 AD, BPT is close to 300 Optics in 500AD, won navigation in 600ish Meet AIs in other continent, they are not that advanced, Willem is the most advanced AI depite he is semi-isolated. He got Liberalism in 500ish. After some trade, here's the tech situation. Trade Astro from Willem. Empire of 12 cities. HE unlocked. I only produced 3 GPS, going to focus on it after NE is online 3 turns later. Tech -- Not bad even in non-isolated map. 800AD save is attached for your reference.