Romans believed in many gods. They were believed to be all part of family and were human like except for the powers they were told to have had.
Maybe you’ll recognize several of their god names: Saturn, Jupiter, Neptune, Mars, Venus, Mercury. Different gods were supposed to be in charge of different areas of life, so you might sacrifice to the one you thought would most be able to help you.
Capitoline Museums [CC BY 3.0]
When they conquered new people, they just took on their gods as well, thinking maybe they could help them.
They did have temples with statues, and priests were in charge of them so that they earned money from people coming and bringing money to the gods and were fed by people bringing food to the gods as sacrifices. When emperors declared themselves to be gods, people had to worship them and sacrifice to them. When Christians refused, they were killed.
People would have small god statues in their homes. You can read in the Bible about the statue makers getting mad at Christians for teaching their was only one, true God. It was bad for their business.
Christianity became the official religion of the Roman Empire by the Emperor Constantine in the 4th century AD. It was probably one of the worst things that could have happened to the Church. Christianity lost its identity as one body that followed Christ and was becoming like him and became something led by a man instead of led by God. Roman leaders weren’t following Christ or the Bible. It wasn’t Christianity, but it took on its name, giving Christianity a bad name instead of the reverent fear that surrounded Christians in the early church. It was the beginning of people using Christianity to seek power and money instead of seeking God and His righteousness.