I assume that you are referring to the Romans here.
I am no expert, but here is what I’ve taken away from my reading.
In our modern morality, the bottom line is that all men are created equal, and therefore have a set of natural rights that must be protected. We decide if something is “moral” or not by reasoning about how it would affect people; different people may weigh different acts differently, or argue about who does and does not meet the definition of a “person” with rights. For example, if you are pro choice, it isn’t because you believe killing is right; it is because you don’t consider a clump of cells to be a living human being with rights.
Compare that to medieval morality, pre-enlightenment (focusing on Europe here); or rabbinical Judaism morality. Morality is ultimately drawn from God’s will/love (Christianity) or God’s law (Judaism). Something like two men having sex doesn’t hurt them or anyone else; therefore modern morality generally accepts gay sex. But religious law can point to Deuteronomy and say “It is forbidden, therefore immoral”.
Interesting side note, nowadays many religious people take the religious argument (gay sex is bad because it is an abomination in the eye of God!) and modify it to meet our modern moral framework. So yes, God said don’t have gay sex; but he must have had a reason for doing so; and since he is God that reason must have been good. We can reverse engineer it and declare “well, I have nothing against homosexuals, but the purpose of marriage is to raise a family and homosexuals can’t do that as well!”. The Ben Shapiro school of debate. But I digress.
So all this crap about modern secular vs religious morality. What about the Romans? I think Roman morality is based around one central pillar: the glory of Rome. You can be as ruthless as you like; if you are making Rome stronger, (or by extension, your own family within Rome’s power structure) you are being moral.
As an example, let us look at the most idolized figure in Roman Mythos: Romulus.
First of all, Romulus’ orgin story shows us what Roman society valued. Romulus is of noble blood, as a well as divine blood. His ancestors include Trojan heroes who escaped Troy’s destruction by the Greeks, and literal gods - specifically Mars, the God of War.
So the Romans value nobility, as well as their deities. Maybe not in a “all morality stems from the words of Jupiter” sense, but instead in a “you can tell this guy is legit because Mars was his great grandpa” sense - the fact that Romans claimed Romulus descended from the gods show that the gods WERE important in their society.
Next up, what did Romulus actually do? Well, the answer is, a bunch of horrible things - but since they made Rome better, they are celebrated. Morality in a Rome First, Might Makes Right sense.
So Romulus and his brother Remus are orphans, raised by wolves and then peasants (but a peasant boy could never found Rome - that’s why they had to be adopted). They grow up, have some adventures, and go off to found Rome. But they can’t agree exactly where the city should go; so Romulus murders Remus. FRATRICIDE! Surely the Romans won’t honor a Kinslayer? Wait, no, they don’t care. Why? Well, because Romulus was right, and where he founded his city was the correct place to put Rome to lead it to glory. So clearly murdering Remus was the right thing to do!
And the next thing the Romans do, in their first act as a city, is invite the neighboring Sabines to a party, then kidnap the women and run off with them (because Rome had many male colonists, but few women for them go be with). This event was called - BY THE ROMANS - The Rape of the Sabine Women.
Yet this event is celebrated, not mourned. Why? Because in the Roman mindset, even kidnapping a city’s female population and forcing them to marry is “right”, so long as it makes Rome stronger.