use workers to build fortresses near your border and spaced 2 hexes apart .... will also need LOTS of arty and a good amount of cavalry and infantry, the latter for defending your forts and cities .... keep forts far enough from your border so his MA needs 2 turns to reach you .... when he moves into your territory, move your arty into the forts and bombard the S_it out of them, hopefully getting many of his units knocked down to a single hit point ... then counter-attack FROM YOUR FORTRESSES (and cities if necessary) with your cavalry ... you should be able to get one hit point most of the time ... then retreat back into fort, and w/draw your damaged counter-attacking units to a city w/barracks ... keep this up and you might wear down his army, and buy yourself some time to catch up with tech .... you probably will lose some of your border towns/cities, but if you can channel his attack toward your line of fortresses, you might have a chance ..... must stock up fortresses with rifleman/infantry, whatever you have, and a few defensive arty .... also, create "killing zones" around your fortresses i.e. cut down forests, clear jungles, etc., and try NOT to build fort adjacent to mountains or hills - do not want to give enemy a combat bonus of any kind ....
the Great Khan wishes you luck, and death to the Persian dogs!!!