Cicero wrote a dialogue called De Re Publica, which has sometimes been referred to as his Republic a la that of Plato, but is more properly translated as "Of the Republic." The Republic in question was that of Rome, still in existence at that time but shortly to be extinguished by the civil war leading to the dictatorship of Julius Caesar, which in turn was followed by another civil war leading to the establishment of the Empire by his grand-nephew and adopted son, known to history as Augustus.
Cicero's work may be distinguished from that of Plato both because it dealt with an actual nation and government (though justice and ideal government is addressed) and because it was written by an astute practical politician and thinker--someone who actually governed, as a senator and consul of Rome. He also had an axe to grind. He wished to point out that good government is contrary to the cult of personality surrounding Caesar, and that Caesar sought power merely through ambition and for the satisfaction of his pride. Plato, of course, was speculating regarding an ideal state, though some like me may think his ideal to be deplorable. It's unclear whether Cicero's work was ever finished and that we know all he wished to say; it has come to us in fragmented form.
Within those fragments is a description of a dream itself described as "The Dream of Scipio" (Sonium Scipionus). The Scipio in question is not the Scipio who defeated Hannibal at Zama, who we know as Scipio Africanus, but rather his grandson, who we know as Scipio Aemilianus. The grandson in turn was given the honorific Africanus as he was Rome's general in the Third Punic War in which Carthage was finally annihilated by Rome (he had the name before then as it was a hereditary title, but subsequently earned it as well).
Scipio Aemilianus was notable not only as a general but as a friend of philosophers, known to converse with them regularly. This practice earned him the public dislike of the dour censor Cato, who thought him far too Greek and frivolous. It may have been his fame as a philosophical sort of Roman which led Cicero, another philosophical sort of Roman, to provide a fictional account of a dream Scipio Aemilianus supposedly had before the destruction of Carthage by the Roman legions.
In that dream, the grandson finds himself in the presence of his grandfather, gazing down on the Earth from a great height, among the stars. They converse, one Africanus to another. Grandpa Scipio tells his grandson of his victory over Carthage two years away, and of his future in general, but also invites him to consider how small the Earth is--a tiny part of the universe. Rome, of course, is even smaller; a small part of the Earth which is a small part of the universe. The living Scipio is asked to reflect on the insignificance of the Earth, of life, of we humans, and understand that our true nature is divine and does not end in death, and we should hold dear only that which is eternal in us and in the universe.
Perhaps this dream is intended to function much as the slave's reminder to those granted a triumph. "Remember you are mortal" are the words supposed to have been repeated to the honored victor by the slave riding with him in his triumphal chariot. The message that all glory is fleeting, soon forgotten, seems to be one which can be derived from the dream.
But it seems something more was involved. Cicero was a lawyer and politician who tried to be a philosopher as best he could. He studied with philosophers and wrote philosophy. We owe a great deal of our knowledge of ancient philosophy to him, as he wrote of books no longer available to us, lost in time. He seems to have been making the point that we should not consume ourselves over worldly matters like fame, victory, conquest and power, but devote ourselves to wisdom, virtue, and ascertaining the laws of nature and through nature, God.
Cicero knew Stoicism well and was sympathetic with it, though we know he did not consider himself a Stoic. This is a Stoic perspective. The quest for fame and power and what goes with them is a quest for things not in our control. When we read Marcus Aurelius we find that he often points out that the great of the past are long forgotten as we will be forgotten after we die, and that which concerns us so much now is insignificant. I think the great schools of philosophy which existed in ancient times agreed on certain things, and that most if not all of them emphasized that the universe is vast and we and all we do is small in comparison; our petty fears and hatreds and desires all mean nothing, and we should concern ourselves only with eternal truths.
But if our world is insignificant, and we are even more insignificant, what do we matter? Why should we try to do anything with our lives? We know now the universe is much larger than any of the ancients could even imagine. From the cosmic perspective, we aren't even noticeable. We may as well not exist. Our pretensions are laughable; our concerns less than trivial.
We know how this question was addressed by Christianity, which denigrated this life and even delighted in its denigration. It profits a man nothing if he gains the world, as our lives, here, are not only unimportant but are sinful. It is only the next world that is significant. So, certain Christian sects even accepted the view that "good works" in this world mean nothing.
That doesn't seem to have been the response of ancient pagan philosophy, though. Stoicism's "things not in our control" were what is of no concern, and the view from above the Earth granted Scipio Aemilianus confirmed this fact. What saved us from insignificance according to Stoicism, it seems to me, was its pantheistic conception of Nature and the belief that we as rational creatures shared in the divine. Christianity held that we and the world in which we live are evil; the Stoics believed we, and the world, are part of and partake in the deity and so cannot be evil. We escape the trivial by virtue of being part of Nature itself, and acting in accordance with the divine reason in which we share.
By acting according to reason, or Nature, we naturally (pun intended) do good works and our actions are thereby significant, one might almost say inherently so. It's when we act inconsistently with Nature that we become trivial.
This seems to me a far nobler and more satisfying response to the vastness of the universe.