Elven was send to buy time for building of Great Wall. They know, that they will fight again brutish orcs, goblins or different savages, but when the time to fight come, they were totally surprised by presence of sort of desert skeletons and monsters. Skeletons seems so out of place that elves thought that they have hallucination by some dire spell.
First volley of skeletons arrows was brute wake up. Empire of Dust seize good foothold in forest for next move and elfs were hard pressed to setup defense line. Dire worm riders flanked good position for bolt throwers on the left side, but they were crushed by elven heavy cavalry. Brave princesses on the right side sacrifice herself by bold charge to bone chariots any stopped their advance.
These two actions buy time for set up overwhelming barrage of elven archers and bolt throwers, which cut down every skeletons attempt to seize the victory.
After few volleys, the skeletons and their monsters lie broken and the victory could be celebrated!