It is said in some websites (This one, for example.) that the Julian Period (the foundation for the Julian days used by astronomers and some software) was derived by multiplying various regular periods, among them the Roman Indication. I’ve Googled and looked at Answers.com and I cannot find anything that tells what the Roman Indication actually is, or how it is derived.
From here:
Thank you. My google-fu must have slipped.
As a side note, is there any indication why Romans assessed their taxes on a 15-year cycle?
Derleth, be sure you see that it’s indiction and not indication if you try to Google for better answers. I was a bit curious about the 15 year thing myself, but never bothered to find out more about it. My fascination with the Julian Period and the Julian Date (as opposed to the Julian Calendar – NOT the same Julian) ended with the numbers involved.
For that matter, I always wonder why one pronounces "indict’ as if it were written “indite.”
My Latin dictionary defines “indictio” in the sense that matters here as a post-classic term for a period of 15 years, named after a land tax collected in cycles of this length. Wikipedia also seems to suggest that the 15 years cycle has its origins not in taxation in general, but in land taxes.
Originally, Roman taxes were collected in cycles of five years: The censores were elected for this period and had the competence to classify every Roman citizen, according to his fortune, into one of several categories based upon which the tax he had to pay was calculated. Maybe later periods switched to three times the length of this cycle for land taxes because land is a very long-lasting commodity that keeps its value over time very stable. Just a WAG.
What would be the 28-year solar cycle referenced there? The solar cycle with which I’m more familiar is about 22 years long, and is often considered an 11-year cycle since the first and second halves are indistinguishable for many purposes.
It’s my recollection that the 28-year period refers to the return of the date February 29 to the same day of the week. In other words, it’s more a calendar cycle than a solar cycle as such. But if one considers the 365.25 day year, with the .25 part being significant, and the leap year solution to that accumulating fraction of a day posting an extra day every fourth year, the 28-year period does make some sense. The fact that it’s not really accurate is another issue from the 28-day “solar cycle.”