Historic cities are pretty much the main focus in Evony. If you are in range of an enemies historic city that can draft you you must make sure your cities are undraftable. Capturing historic cities pretty much gives you control of a section to the map. There main benefits are being able to draft players cities for troops. But there are also other policies which are useful such as population redeployment and disarming player troops. Historic cities are relatively easy to Capture providing you have the troops to take them as well as the heroes to lead your waves.