Not sure if this has been mentioned already.

Sounds

Archers seem to have infantry marching sound and infantry seem to have Archers marching sound.

Archers make the intimidating 'crunch crunch crunch' noise as they march, wereas infantry just rattle and barely make a noise.

The Mongols

In my game the mongols just parked above the black sea, until about 50 years later I sent a scout to check them out. Then they rampaged across Eastern Europe.