Here's a nice challenging map for online multiplayer. You can still fight against computer opponents, as long as you choose opponents that build smaller castles. Three different resource profiles can be found in the download - it's the same map layout, just different amounts of resources:
All you have is grass, but there's lots of it. Increasing and taxing population is a good idea.
CORRIDORS, low resource
All resources included, in small amounts. 2 iron, 1 stone, 38 trees.
CORRIDORS, high resource
Plenty of resources, make that army huge!
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