The Genius was the individual instance of a general divine nature that is present in every individual person, place, or thing. Much like a guardian angel, the genius would follow each man from the hour of his birth until the day he died.
Although the term genius might apply to any divinity whatsoever, most of the higher-level and state genii had their own well-established names. Genius applied most often to individual places or people not generally known; that is, to the smallest units of society and settlements, families and their homes. Houses, doors, gates, streets, districts, tribes, each one had its own genius.
Lararium
A Lararium was family shrine, normally located in the atrium of the house, which honoured the Lares and the family Genius. Each Lararium features a panel fresco containing the same theme: two peripheral figures (Lares) attend on a central figure (the family Genius).
Hundreds have been found in Pompeii.
Digital Maps of the Ancient World 