Although the first people who came to the Mediterranean were probably following along the coast, and ate mainly fish, shellfish, seaweed, and wild figs, by the time the Roman Republic got started, there were far too many people in the Mediterranean to be able to live entirely from the ocean, and although people kept on eating a lot of fish and seafood, most people had to also eat farmed foods.
So most people in the Roman Empire lived mainly on the usual foods of people living around the Mediterranean Sea – barley, wheat, and millet, olive oil, and wine, which we call the Mediterranean Triad. In addition to being full of carbohydrates, these foods provided fat (the olive oil) and protein (the barley and millet). Poor people ate more millet, and rich people ate more wheat. Starting around 100 AD, poor people started to eat oats, too. If you were poor, you would also eat vegetables like lentils and cucumbers, onions, garlic, and lettuce, fruit like apples and figs, nuts, and sometimes cheese and eggs.
People also ate different food depending on where they lived in the big Roman Empire. In Egypt and West Asia, most people didn’t eat pork. In northern Europe, some people drank beer instead of wine, and got their fat from butter instead of olive oil.
Another difference was how rich you were: rich people ate different food from poor people. There weren’t very many rich Romans. Most people were poor.
But some rich Romans were REALLY rich and they liked to show it by having a lot of slave cooks make them very very fancy dinners, and then inviting a lot of their friends over to eat with them in fancy dining rooms. They tried to serve food that was unusual or very expensive or very difficult to make. In fact, these things were more important to rich Romans than food that tasted good!
We know about rich Romans eating whole plates of peacock tongues, for instance. One complicated meal involved stuffing a chicken inside a duck, then the duck inside a goose, then the goose inside a pig, then the pig inside a cow, and cooking the whole thing together. If you were rich, you could also eat beef, pork, lamb, chicken, and fish, dormice, and snails. Sometimes rich Romans sent slaves running up into the mountains near Rome to get snow, so they could have slushies even though there were no refrigerators!
We know some of the recipes rich Romans liked from a Roman cookbook written by a man named Apicius in the time of the Roman Empire (we aren’t sure exactly when). Apicius’s cookbook still survives today, and you can find some of his recipes online.
A warning though: Most modern Americans don’t like these recipes very much. Romans liked to make spicy sweet things, which Americans don’t usually eat.
The Classical Cookbook, by Andrew Dalby (1996). Both rich and poor people’s recipes, with a lot of context too.
A Taste of Ancient Rome, by Ilaria Gozzini Giacosa (reprinted 1994). Recipes from Apicius, including the weird ones.
Ancient Roman Feasts and Recipes Adapted for Modern Cooking, by Jon Solomon (1977). A history of Roman food, and then about a hundred Roman recipes you can make.
Around the Table of the Romans: Food and Feasting in Ancient Rome, by Patrick Faas (2002).