#greymarch

Beginning in familiar territory then, and going back every thousand years:

The Third Era Greymarch, or, The Final Greymarch: 3E 434 (because I don't see how the HoK can realistically tackle all major questlines and DLC to completion within the last four and a bit months of 433 the game gives us.Adjust the following dates by a year if you don’t agree.)

The Second Era Greymarch: 2E 330

The Last March of the First Era: 1E 2250

The Middle March: 1E 1250

The Earliest First Era Greymarch: 1E 250

At this point the Greymarches fall back into the Merethic Era, where precise dates are difficult to nail down, and few numerical dates in general are offered by the UESP Wiki and in-universe lore. This is also where the years date backwards, starting from zero.

The last Greymarch of the Merethic Era occurs at some point during the midst of the Late Merethic Era, likely around ME 750

If so, then the preceding Greymarch happened around ME 1750, either in the latter part of the Middle Merethic Era, or in the early years of the Late Merethic Era

Prior to that is the earliest Greymarch we can put a rough date to; ME 2750, which technically puts it before the start of the Early Merethic Era at ME 2500, but that date is used only because the oldest known Mundus construction, the Direnni Tower (where the et'Ada hold their Convention, set the laws for Mundus and end the Dawn Era), dates back to ME 2500, and the Shivering Isles are outside of Mundus. Maybe its the early Early Merethic Era *shrug emoji*

Before the Merethic Era came the Dawn Era, where assigning dates to Greymarches becomes impossible, as linear time as we know and understand had not actually technically been established yet, therefore all dates become arbitrary in this age.

All we know is that there have been seven, possibly eight, record-able Greymarches all together, with no knowing just how many occurred during the Dawn Age.

It is probable that there was at least one, however, as The Predecessors state “The ruins fell into distinct periods, each period separated by exactly 1,000 years from the other (although Cylarne remains the exception, being many thousands of years older than the next oldest extant ruin - suggesting only that the ruins from many earlier eras lie waiting to be discovered, or have been lost to the ravages of time).”

As one of the loading screens for the Shivering Isles DLC states: “The ancient city of Cylarne is believed to be the original capital of the Shivering Isles.”

Together this information suggests that Cylarne was first founded at some point during the Dawn Era and likely met its doom during that period as well. As their ruins are dates to be much older than other ruins in the SI, and time as we know it doesn't exist in the Dawn Era, then who is to say a thousand years didn't stretch longer than “normal”. Time could compress and/or stretch beyond the limits of mortal imagination and comprehension, and Greymarches could thus happen more frequently or not, and no-one has found the ruins yet. Who knows? There's bound to be at least one that happened, that much we could be reasonably sure of.

My current Greymarch timeline

3E 434

2E 330

1E 2250

1E 1250

1E 250

Late ME 750 approximately

Middle ME 1750 approximately

Early ME 2750 possibly

Dawn Era ???

Conclusion

Whether you subscribe to the thousand year theory, or the once an era theory, you still end up with multiple Greymarches either way with an unknown number in the Dawn Era

Instead of happening at the end of the era, as Sheo himself says, perhaps happens at least once every [mortal] era, or mini-era if you split the Merethic era into it's three main stages (early, middle, late).