For the tactical scenario, you could have a group of elite (and well supplied) Persian archers holding a small hill that's right in the path of the Spartan advance. The Spartans have no archers and few, if any, slingers and have to climb a rough hill to get at the Persians. The Persians wreak havoc on the Spartans advancing up the hill with little formation, but the Spartans can't advance past the Persians or they'll all be vulnerable to fire from the rear.
The Persians hold the hill for a long day, with piles of Spartan dead on the slopes. They only fall when the last of their arrows runs out and the Spartans make it up the hill in enough numbers to overwhelm them.