This is a real ancient Byzantine hand grenade!
In what was likely the original invention of the grenade, the Eastern Roman (Byzantine) empire realized that their "Greek Fire" (invented in the prior century) could be deployed as a hand-held weapon. Until that point, in roughly the 8th century, Greek Fire was deployed exclusively by early flamethrowers.
The exact composition of this incindiary weapon was such a closely guarded state secret and it remains unknown to this date. The effects of Greek Fire technology, which could burn on water (to the great detriment of enemy ships), had such a profound effect on their adversaries that the Crusaders would go on to call any powerful incindiary by this name.
The original names for this technology were varied but some translated to "Sea Fire", "Roman Fire", or "Sticky Fire".
We can ship this ancient armament worldwide!