What were the main garments, clothing styles, and silhouettes worn by men and women during the Ancient Rome--Roman Republic to Roman Empire?
In a way that clearly imitates the style of the Greeks, the Romans also had four basic pieces of clothing which would befit both males and females.
Ancient Rome's basic fashion styles came in the form of tunics, stolas, sandals and belts.
Tunics were the basic pieces. It is generally known that a tunic is a long piece of clothing that goes past knee length. Most married women would wear a tunic of ankle-length. The tunics were sleeveless and, to protect women from the elements, the stola would be used. It is a longer piece of clothing that covers the tunic. These could be belted either over the tunic, or the tunic could be belted and then the stola be belted as well, making a double belt. Sandals (like the Greeks) were the "staple" footwear of the time.
Men had a similar style. They would wear belted tunics and, to protect themselves from the elements, they would wear a cloak over it. Sandals were also their choice for footwear.
Notice how both, the Greeks and the Romans, were simple and predictable in their style of clothing. This made it easier for them to produce their clothing by looming it at home, a job mainly done by women or slaves. This is why the clothing style of both cultures is so easy to reproduce in modern times, particularly for historical non-fiction presentations.