In my first game as Babylon, I started with my standard military focused build: Scout, Scout, Slinger, Slinger, Slinger (or Archer if available). My first slinger killed an barbarian unit and got me a eureka for Archery (Babylon gets the full tech). I upgraded the two Slingers to Archers. When I finished building a third on about turn 20, I got the eureka for Machinery during the Ancient Era! After clearing a couple of barbarian camps, I had enough gold to upgrade one of my Archers to a Crossbowman. Do you know how easy it is to take down city defenses with a Crossbowman in the Ancient Era?