Using the CK2+ mod, with the ancient religions by culture setup option, 769 date--
As the Duchy of Latium (as that title is held by the Pope before the setup-options were applied when I unpaused, I used the console to give my character the title),
- I survived, just barely, the attempted subjugation by my father-in-law, the King of Lombardy (I'd hoped that marrying his daughter would give me some breathing room)
- Pops died a couple of years later; I was able to declare a war of conquest against he minor heir. The particular CB ended up usurping the holdings of all but a few of the Lombard dukes/counts, so in one fell swoop, I controlled most of Italy.
- Rather that revive Lombardy (which would have become Italy, as mt character was not a Lombard), I created a custom kingdom.
- I eliminated and/or subjugated the few remaining Lombard counts ... in the meantime, surviving (again, just barely) and attempted conquest by the Karlings.
- During civil war distractions in the ERE or among the Karlings, I picked up some of the ERE holdings in Italy and Province and Septimania -- the goal at this stage was to get three Roman Holy Sites, so I could create the Pontifex Maximus.
- A refugee with a claim to a county in Tunisia came to my court. I converted him to the Roman religion, landed him in Italy and pressed his claim. After the truce expired, I was able to use that county as a base to take the whole duchy of Tunisia.
- Sometime later, the P.M. called a Roman Great Holy War against Africa ... and I picked up everything from Tunisia to Egypt.
- Then I took Alexandria. When that truce expired, I picked up half of Sinai.
- This put me close enough to Jerusalem to go for the 1/2 controlled by that small realm. The Abbasids (pagans, not Moslems) had the other 1/2 of Jerusalem; but by them I was able to take them on.
= So, it's just short of 100 years into the game. My current ruler (my realm is now a custom empire) inherited a claim to the throne of the ERE. They are weakened after a series of civil wars, and the current Basileus is not yet crowned ... so, I'm about to swoop in. Once I take the ERE, the only remaining duchy required to reform the RE is Antioch, held by the Abbasids.