Heya! As a writer of historical fantasy, I figure I'm close enough.

In stories set in historical worlds, definitions can include stuff like what people ate, what they wore, what their houses looked like (for example, square/rectangular houses didn't come to Ireland until the Medieval era; they lived in round houses until then), etc. What were the clothes made of? What is the government like? Armor? Etc.

Also, you could describe the prophesy as your object. If it's real, you do actually have an element of fantasy because real prophesies are a product of the fantastic. If it's not, but gets fulfilled via the efforts of people attempting to fulfill it (i.e. a self-fulfilling prophesy), explain where it came from and how it will affect your story.
-Quaddy

Check this Out!

The Earth Rising Quartet  (XGC) Five-hundred years ago, Earth lost its rebellion. Now it's time for it to rise again... #1837269 by Professor Q

Come Join In!

The Dissolution of Alkonost   (GC) A desert metropolis falls and magick fails in its seams. Who dares rise to save it? #1968212 by Professor Q

Best Contest Alert!

FORUM

October Novel Prep Challenge  (13+) A month-long novel-planning challenge with prizes galore. #1474311 by Brandiwyn🎶