No World Timeline

There is no single shared chronology sitting over the whole world, with one set of named periods every culture gets slotted into. Each culture keeps its own periodisation, on its own internal logic, and the game never states where two of them line up in absolute terms. That absence is deliberate, not an unbuilt feature.

The alternative that was rejected: one timeline, many cultures

The obvious, cheaper design is a single world calendar: Bronze Age, Iron Age, whatever the setting calls for, with every culture's history plotted against the same fixed axis. It was rejected because it hands the player a synchronisation the discipline being simulated never actually has. Real archaeological chronology is built culture by culture, site by site, from relative stratigraphy and costly absolute dating, and cross-culture synchronisation is itself a claim that has to be argued for, not a background fact a player is entitled to read off a shared axis. A world timeline would quietly give away the one class of inference, "did these two things happen at the same time," that the whole game wants to be a real, earnable piece of work.

What a culture's own periodisation actually is

Each culture generates its own sequence of phases, named for what characterises them internally, an expansion, a settlement, a period of contraction, built from that culture's own trajectory across its attribute dials. Two cultures' phases don't have to correspond to each other in duration, character, or position, because there's no shared clock forcing them to. Culture A's expansion can sit entirely inside Culture B's settlement period, and nothing in the data structure asserts that relationship one way or the other. If a player wants to claim it, they have to build the case for it from evidence, the same way a working archaeologist would.

What this costs, on purpose

Relative dating within one culture's own sequence, this layer sits below that one, is genuinely free; it costs no design compromise to make available, because it's just reading the strata that are already there. An absolute date, and any claim connecting two different cultures' timelines, is expensive by design: it requires either an in-fiction dating method (costly, error-bounded, sometimes destructive of the very evidence being dated) or a real, arguable inference chain the player has built themselves. Arguing that an accepted chronology is flatly wrong, that a framework has been stretched further than its evidence actually supports, is one of the highest-scrutiny claims available to publish, precisely because so much else in the corpus quietly assumes that framework is sound.