This scenario is more about resource management than anything else, especially since you can't build Markets. Don't be afraid to re-task your Villagers, and keep your eyes on the 10,000-gold prize.
Ugh, 75-unit population limits again? Whatever.
Marcianopolis will attack immediately, so dispatch your Tarkans north to drive them off. Send one Villager east, one south, and one southwest to round up some sheep; send the Monk west to grab the Relic at the end of the mountain range, and make sure he has a Monastery to store it in. Now build a Mining Camp -- with a Watch Tower to defend it from harassment by Philippopolis -- at the stone mines to the southwest, near where you found the sheep.
By the time you run out of sheep, you should have about 700 stone. Use your shepherds to block the Gate of Marcianopolis with a Castle; otherwise they'll swamp you with Scout Cavalry and Men-at-Arms. Once the Castle's built, the shepherds/builders can be assigned to farming, while your surviving Tarkans circle around your town to clear out any enemies that snuck in before.
With your base secure, you can finally focus on buildings like Archery Ranges and Universities, while doing some exploration and research. Except for Atonement and Heresy, no Castle Age technologies are expensive enough to seriously affect your gold income, so have at it! Keep your Tarkans in the Castle and train two or three Light Cavalry for reconnaissance. Note the gold deposits on the peninsula south of Constantinople: this will be a good place to send your miners when their stone runs out.
A force of two Battering Rams, two Monks, 10 Cavalry Archers, and 15 to 20 Light Cavalry will suffice to raze either Marcianopolis or Philippopolis. But Philippopolis has a second Relic nearby, so go after them first. To properly motivate Constantinople, you're aiming for total annihilation in both cases...even after they resign.
Replenish any losses among your Light Cavalry, and send them across the river to a Monastery which Constantinople has conveniently placed far, far away from its walls. Destroying it will net you a final infusion of tribute, but Constantinople will at last be goaded into attacking you. However, since all the troops they send are Monks, Crossbowmen, and Onagers, your Light Cavalry can either outrun them or hack them to pieces. It should only take a few more minutes to win the scenario.
[This message has been edited by Leif Ericson (edited 07-04-2016 @ 09:53 PM).]