Knowing what the ancients discovered about elements is difficult. We can decipher ancient texts, but only a fraction of what they truly knew made it to the present day. Most of what they knew wasn’t transcribed, and what was set in papyrus, stone tablets, or manuscripts either crumbled with age or was intentionally destroyed.
But we have bits and pieces that give us a look into the mind and methodology of the ancient scientists. We can trace alchemy a long, long way back, and we can see that monatomics were very important to religious and medical traditions around the world. They probably even used them in important ceremonial rites!