Disclaimer: I do not own any of the Riordanverse, except my headcannons.

Summary: "The Greeks and Romans are fundamentally different, Jason. There is a reason they didn't get along,"

OR

Jason Grace does not understand why so many things about Greeks and Romans are polar opposites. It's like the universe wanted them to fight from the start, and that makes no fucking sense. Hermes, ever-helpful half-brother (and available at the time), explains.

OR

Literally just my headcannons.

It was a calm day at Camp Half-Blood (or, as calm as it could be when children of gods were involved – he was pretty sure he heard Clarisse screaming). Jason was taking a walk by the creek, taking some time for himself, when he noticed the crack on the ground. When he first came to Camp, he was told that it was from a fight between Percy and Thalia. He hadn't thought much of it then.

But now that the Giant War was over, Gaea defeated and the Civil War 2.0 averted, he wondered what would happen if something like this had happened at Camp Jupiter. To him, there was an easy answer: it wouldn't happen. Roman training and Roman discipline meant that fights to that scale were impossible. Yet, everyone said that Percy and Thalia hit it off from the first moment, were more sisters than just best friends (and some part of Jason wondered if his sister had replaced him before he shut that out. She had searched up and down for him. She had thought he was dead.), so why would they fight badly enough to produce a crack on solid ground?

"That would be their natural instinct."

He noticed the jogger with salt-and-pepper hair and a grin he'd seen on most Hermes and Mercury kids. He looked Greek today. He'd probably come to visit his children.

"Lord Hermes," Jason greeted. "Are you reading my thoughts?"

"Well, they were rather interesting." He paused. "Did it bother you?"

Yes. Anyone reading his thoughts would bother him. But! Jason knew better than to say that to a god's face. "Not at all," he lied. Which was stupid, because Hermes was a god, the god of lies, and he would definitely know.

Then, he had an idea. An idea that was so impulsive, so impertinent, that he knew that he wouldn't even have entertained it before going on the quest to the Ancient Lands. This must be Percy's influence, he thought somewhat humourously, or Leo's.

"What did you mean, 'their natural instinct'?" He asked Lord Hermes.

Weirdly, instead of getting annoyed or angry, the messenger god just grinned. He clapped his hands and smiled widely, as if discussing his favourite series.

"The Greeks and Romans are fundamentally different, Jason. There is a reason they didn't get along," He began explaining, "Greeks and Romans are simply hardwired differently.

When the West moved to Rome, we gods changed. That's nothing interesting, of course, gods always change to some extent as per the nature of the current heart of the civilization. Romans were militarily inclined, so we became a little more… controlled. Strategy, discipline, order, and things like that became more favoured. You, Roman demigods, reflect that aspect. The thing is, we never underwent that huge of a change while moving anywhere but Rome. Artemis says it's something about the first change, but it could be anything. So, after that, there were always two aspects: Greek and Roman."

"That's the how, not the why," maybe Jason did want to get incinerated after all. Curiosity did not mean doing the stupidest things to reach answers, and yet, here he was, risking combustion.

This is your fault, he mentally complained to his impulsiveness.

"Yes, yes. Have patience, little brother. Right, where was I? Yes, the difference. So, because the gods changed, what they passed down to their children changed too."

That made some sense.

Hermes continued, "Roman demigods, they are usually more responsible. Discipline and order, that's their thing. Less likely to blow up at something, and less likely to blow up something, all that. Now, don't get me wrong, you lot are completely capable of being more, ah, chaotic, but part of your genes just don't like that idea. You like structure."

"Explains why it's said Romans are great at building things."

"Exactly! See, now you're getting the hang of it. The Greeks aren't like that. Their blood is, for lack of a better explanation, more ancient than yours, because we began in Greece. Athena likes to say that they resemble us as we were in the ancient days."

"And how were you?"

Hermes smiled again, but this time, it seemed more threatening. "Dangerous. Chaotic. Merciless. Today, we could be considered extremely laid back, and most of the time, the demigods reflect that. But, at times, their divine heritage comes to the forefront enough that it is as if they learned that from us. You Romans have the potential ability to be like that too, if not to the same extent, but your very instinct holds you back from going there."

Part of Jason wanted to argue that the Greeks were extremely nice. There was no way that they could be described as merciless or basically more powerful than the Romans were.

And yet. He remembered seeing them in battle and hearing stories of other battles.

Clarisse was known for slaying a drakon by herself, fueled by her anger, her grief, and the blessing of Ares.

Piper had brought his soul back from the Underworld. Charmspoke his heart into beating again after Hera went into 'Her Majesty the loose cannon' mode. Didn't that mean that an Aphrodite child with strong charmspeak could also ask someone's heart to stop beating, for someone's soul to leave their body?

Hecate children could do magic to a level which was unheard of to Trivia kids.

He was pretty sure he'd seen Demeter kids raise carnivorous plants from nowhere, and use normal plants as strangulation devices. Also, he remembered an incident when all the plants except the dryads of Camp Half-Blood died off, only for everything to turn normal within a day (note to self: never provoke Katie Gardener).

Once, during the Titan War, Pollux had apparently dealt with the monsters by tapping into Lord Dionysus' power over madness.

And then there were the Big Three kids. At first, Jason had been jealous – their power, to him, seemed much more advanced, even though he'd trained for longer. Maybe, he had thought, it was because he trained more with weapons and less with powers – he couldn't fry Legionnaires because his aim was off. But, Hermes' explanation made him rethink that. Was it just because their blood was, apparently, older?

He remembered seeing Nico di Angelo, who walked everywhere with shadows clinging to him. He could summon the dead and order them to do his bidding, and they would. Reyna had told him she had seen the boy turn Bryce Lawrence into a ghost with his powers. (Not that this made Jason mistrust him; he was a good friend and a useful ally.)

He remembered his sister, Thalia, with her tendency to electrocute people when mildly annoyed, and call upon entire storms (lightning, rain, thunder and all), the storm raging around her and her body positively crackling with electricity.

Jason had also heard of and fought alongside Perseus Rhea Jackson. She could command hurricanes and tornadoes, cause earthquakes when angered, and control water in every form. If she could control poison and ichor, blood wouldn't be difficult either. If either of their genders were switched, sometimes Jason couldn't be blamed for mistaking Percy Jackson for her father.

But usually, they were all kind and welcoming, preferring having fun and joking around. That didn't mean they weren't dangerous.

"You get it now, don't you?"

Yes.

The Romans would build structures and other things, an army, an empire, and use those to defeat you, to crush you. It was their method, learned from the teachings of the Roman aspects of the gods. The Greek demigods were like their godly parents, in that they would simply destroy you.

(Even then, Jason couldn't help but think that the Roman way was better, safer. Not completely because of inherent superiority, although it factored in, but because the idea of being that destructive scared him. What if someone reached a point of no return? There was no rigid military training to hold them back. He couldn't help but wonder if the Greeks had to pay attention to themselves at every moment of every day, to make sure they were okay and they were in control. He wondered how worse it was for his cousins.)

Romans learned from the gods, and Greeks resembled them.

A/N: okay, so this idea came to me this morning and the headcannon had been swimming in my head for much longer. It even explains the different training methods and some differences i saw between in them in books. also, it's simply a personal opinion that greeks might be more powerful, or at least tap into their powers more, than the romans, who were more into the military training regime. The idea of the blood being older comes from a mentioned line in the fic 'down memory lane' by wolfieriddlee.

Also, i'm thinking of crossposting on AO3 under the alias duchessina. (once i get the invite)