Why this mod?

CKIII, at its publication, already possessed several characteristics inherited from CKII. Unfortunately, some of the assets introduced by Holy Fury have been removed for no apparent reason: for example the Hellenist restoration, one of my favorite decisions.
Either way, it's not very clear why - the content present in Holy Fury has been imported in CKIII for its bigger part, and getting around the in-game prerequisites for Hellenism is easy, just create a custom character and choose the ancient Greco-Roman religion.
While these features will be probably reintroduced with future DLCs, there is no real reason to wait some years to have it back, since most of it is already in the game.

“In the Heart of the Mediterranean” aims to allow these choices with the greatest possible compatibility, because ITHOTM is created with the intent to not replace any file of the base game or alter any mods added by a player to his/her playset.

The mod also used to allow the player to restore the Roman Empire as an Abrahamic religion different from Christianity (Islam, Judaism and Dualism in game) before the vanilla game (finally) removed these restriction with the 1.10 "Quill" patch.

So what does “In the Heart of the Mediterranean” (ITHOTM) introduce?

-Restoration of the Hellenist religion as a Latin or Eastern Roman ruler.

-Creation of the Empire of Italy as a non-Christian ruler for mods that do not have the present empire as de jure on the map. (this decision has been removed temporarily, as most big mods still need to be updated so it might be no longer needed)

Is ITHOTM achievements compatible?

Yes, it is. And I'll try is to keep the mod compatible with them as long as possible, without interfering with the main objectives of ITHOTM itself.

Why is there a time limit to the conversion to Hellenism?

The time limit has been established because beyond those dates, I believe that there has no longer been, univocally, a “living” Hellenist tradition.
In Italy in 1328 an earthquake caused the Sibyl's cave to collapse and the church decided to intervene after the fact, putting an end to the religious practices of the Sibilla Appenninica's sanctuary, the last loosely organized remnant of the Greco-Roman religion in Italy.
And in the Peloponnese, after the 12th century the Christianization of the inhabitants was mostly completed.
The Beneventan witches were active as late as the Counter-reformation era, well beyond the game time frame, but of course is very well reasonable to say that the more time passed, the local beliefs morphed from the Hellenist ones to syncretism with folk Christianity.
Although, clearly, reconstructing a Hellenist religion would have remained theoretically possible based on the large corpus of classical works accessible both in the Latin west and the Eastern Roman Empire, especially in the context of the game in which one's character is a politically influential noble, there is enough time, with both two bookmarks, to make the decision without the player feeling trapped in a desperate battle against time, if he/she wants so. So there is no need, in my opinion, to add a fallback decision for the late Middle Ages.

But wasn't Hellenism a religion already dead and defunct in the Middle Ages? The game says so.

If by dead and defunct it is meant as being not a majority religion practiced by one or another ruling dynasty of the time or the state religion of a political entity, yes, obviously Hellenism can be considered a dead religion as CKIII suggests.
As a traditional faith practiced by a minority of the population in the regions of Greek or Latin culture, definitely not (but surely wasn't “in good health”, of course), especially in the first centuries of the Middle Ages. In addition to the majority religions, there were numerous minority faiths during the era covered by the game, although these do not necessarily appear on the map as they had a relatively limited number of adherents; the Hellenist “remnants” were just one of them.

Why can't the Holy Roman Empire reunify Rome if the emperor is not a Christian?

The Holy Roman Empire was born as a Christian state and apart from the brief parenthesis with its capital in Palermo under the Hohenstaufen, it has never been a state centered on the Mediterranean or based for most of its history in traditionally Romance speaking lands (its heartland was modern Germany and later Austria). In this case I agree with the base version of the game that sets this limitation.

Why was the restoration of Roman culture not added to the possible decisions?

Because Roman culture never really “died”: there is no clear demarcation line between the classical one and that of the medieval (and modern) Romance speaking nations and no history of massive population displacements either; in most of the western portion of the Empire, the Germanic conquerors integrated themselves in the local late Roman culture.
In terms of language spoken, the divergence from the classical Latin of Caesar, Cicero, Virgil or Seneca was already in progress well before the fall of the western part of the Empire; the culture that is usually associated with "Romanitas", the classical one, was Hellenistic and therefore, it had disappeared from the main urban centers before the fragmentation of the western provinces into the Roman-barbarian kingdoms. The only thing that significantly changed with the collapse of the empire was the faster linguistic divergence from literary Latin and the vulgar Latin spoken daily in the former provinces.
However, Latin never fell out of use and remained the written language of administration and culture for much of the era covered by CKIII in Southern and Western Europe, as well as being the sacred language of the Roman Catholic Church. Latin as official (“court” in game) language started being replaced by Romance languages only at the very end of the game, and this happened exactly because no ruler ever managed to restore any enduring unity in the Latin speaking countries.
While re-unifying the Empire would have probably resulted in some official Roman culture for the imperial court and the high nobility, I don't believe in the possibility of half millennium or more of local culture suddenly disappearing, old fashion being suddenly new again (togas, for example, fell out of daily use already in the 2nd century, during the Classical Age itself), or the general population of a largely illiterate society switching to everyday use of a literary, scholarly and courtly language.

How and until when will the mod be supported?

I intend to support the mod as long as I have a reasonable amount of free time (and there should be no problem with that) and until the base version of the game or some mod that I follow adds the options present in ITHOTM to CKIII, making my mod superfluous.

Future developments

My long-term goal is to add, if possible, without rewriting the religion files, a way to use Roman names for the Hellenist gods when the player's character is Latin and not Eastern Roman.
As this is my first mod, at the moment I have no idea if it is an easily achievable objective, so I preferred to publish the current version which uses the vanilla Greek names for the gods.

I want to clarify that the mod will not be expanded to include a substantial number of additions, because its goal is to unlock some alternate history possibilities that I feel are important, but, at least for the time being, not to add further content, which both the official DLCs and several mods are already providing.

Why is Hellenism not reformed like Basque paganism by converting my character?

Unfortunately, the decision of restoring Basque paganism automatically reforms the faith, but if a player wanted to reform it again, he/she would then have to use a generic symbol for the religion. So I preferred to leave the faith unreformed, allowing the player more freedom of choice while keeping the Hellenist symbol as it happens with the reform of the other unorganized faiths in the game.

Can the AI take the mod's decisions?

No, the AI won't take any of the ITHOTM decisions. The mods now contains only the Hellenist faith restoration, and this would have been a very unlikely decision for any medieval ruler; while at the time there were still alive remnants of the Old Religion, and a conspicuous number of texts from the Classical age survived christianization, the large majority of the population in the territories part of the Roman Empire or its former ones were inhabited by large Christian or Muslim majorities, making a return to the old ways politically inconvenient to say the least.
So, this undertaking is reserved for players only, to not make alt-history results too frequent in game.
In the future I plan to add a game rule to let or not the AI chose to restore Hellenism.

Why the custom decisions to restore the Roman Empire have been removed?

From the 1.10 "Quill" patch, the base CKIII game already includes the Roman restoration decisions for all the Abrahamic faiths, so my mod ones are no longer necessary. They were very specific to allow the same freedom of choice available to a Christian ruler and now they would only feel as unnecessary duplicates.

Can I contribute to the mod?

The mod currently needs translations into other languages, as it is only available in English. Any translation help is more than welcome.