heres the context for this
while ive known about cannae being a unmitigated slaughter since i was a wee teenagerone aspect of cannae that was not readily apparent to me until recently for whatever recently, was the sheer NUMBER of men killed. ~70,000 men dead in a single days fighting annihilating the roman army of 16 odd legions.

Needless to say this blew my mind.

What blew my mind more was that based on a bit of googling. i cant seem to find another example of a singular battle being that monumentally bloody until we hit the napoleonic wars with leipzig, or the first battle of the somme in 1916

of course rome has had its share oftotal devestating defeats, teutoberg forest and carrhae being notable examples,

i would have thought of platea of gaugamela being a higher body count due the humungous size of the persian force but it seems the issue with gaugamela is we cant even decide how many men the persians had at all

Does anyone else have some contenders for the title of 'bloodiest day of battle in history? maybe a battle in the renaissance, ?

There are quite a few battles of that scale throughout history, we just tend to question numbers much more when it isn't something famous like cannae.

Off the top of my head the first ones that come to mind are these:

Yarmouk where the Roman army was almost destroyed by the arabs

Manzikert where the Roman army was also almost destroyed, though this time by turks

And Achelous, where the Roman army was destroyed in it's entirety by bulgarians

Wikipedia, though not exhaustive, has a pretty thorough page on this topic (including noting where the numbers are in doubt):
https://en.wikipedia.org/wiki/List_of_battles_by_casualties