Atheism wasn't really... a thing, for much of human history. Certainly not before the Enlightenment, and even Enlightenment philosophers generally erred more on the side of deism than straight up atheism. I could go more in depth, but I'll just link to a response by /u/XenophonTheAthenian to almost the same question several months ago here.
To sum it up, the idea of a secular state divorced entirely from the religious world is a concept that people in the ancient world just didn't have. Religion was much more tied up in rituals than it was in belief, so as long as you went through the motions, you could get away with saying just about anything.
Oh, and btw, your first spelling was correct.
It depends on how you mean by "atheism". If you mean simply not believing in the traditional gods, that was fairly common. Euhemerus, a Hellenistic philosopher who argued that the gods were actually great kings who later stories portrayed as gods, was very popular and influential in Rome. Stoic and Epicurean philosophy by no means necessarily denied the existence of gods, but they certainly could, and Lucretius, for example, is scathingly critical of religious practice. Ridiculing myths and beliefs (and the peasants and foolish who believed in them) was quite common--one famous story has a philosopher who is shown a set of monuments erected by sailors saved by Poseidon ask where all the monuments erected by the sailors who weren't saved by Poseidon were. "Zeus Rants" by the well known satirist Lucian is essentially an extended mocking of people who believe the gods are really a thing, or at least something that exercises influence on worldly affairs.
Whether this constitutes atheism in a modern sense is up for debate.
The teachings of the Greek philosopher Epicurus were quite popular in Rome and his words
“I was not. I was. I am not. I do not care” are recorded on many tombstones.
He was not an atheist in the modern sense, there really was no such thing in ancient Rome.
But he did not believe in a soul or an afterlife, and while he believed in Gods he did not believe that they deserved or required worship.