Roman homes had no windows until much later. Instead, the air and light came from openings in the roof. The main room, the Atrium, was the center of domestic life. It was reached by passing through a vestibule. Other rooms opened off the atrium, and I'll discuss those later.
Three elements important to the atrium were the hearth, a symbolic bed, and a place to display the family lares, which are the ancestral spirits and representations of the pagan gods and goddesses the family worshipped.
The hearth may be burning or not, and might even contain a fire brought directly from the Vesta fire tended by the Vestal Virgins.
The bed, originally used for the oldest esteemed member to sleep on, later became a symbol of family continuity. For a wedding, it was decorated with flowers and costly bedding in hopes the symbol would promote fertility and many sons.
The lares were displayed on an altar, the spot where ceremonies took place, like this picture.
Other furnishing, beyond the specified three, might be couches and a marble bust of the owner or distinguished family members.
In the middle of the room was a sunken pool which caught rainwater and distributed it to an area below the floor. In cooler climates north of the Mediterranean, pipes carried heated water beneath the floor to warm the house. The early Romans were engineering geniuses, not only with their aqueducts and underground storage facilities, but also with their home construction.