The Lar Familiaris was a domestic guardian spirit who cared for the welfare and prosperity of a household. A household's lararium, a shrine to the Lar Familiaris, usually stood near the hearth or in a corner of the atrium. A lararium often had the appearance of a cupboard or a niche containing a small statue, a niche painted on a wall, or a small freestanding shrine. Sometimes the Genius of the head of the household, pictured as a bearded or crested snake, or as a man with the fold of his toga covering his head, is depicted with the Lar.
References to domestic religious practice often pair the Lares together with the Penates. Penates, although also domestic guardian spirits, were more specifically protectors of the master of the household and his immediate family. The Lar Familiaris, on the other hand, protected all household members, free or slave, and was associated with a particular place, thus did not accompany a family who moved. Tradition holds that a family's Lar would generously help those who honored him by devotionals and sacrifices, but would turn his back to those who would not offer him thanks or neglected him.
A story about these spirits occurs in the Aulularia of Plautus (Lines 1-36). In the tale, a grandfather begs his Lar to hide the family gold, so the Lar buries it in the hearth. When the grandfather dies, the Lar did not show the son where the gold was hidden because the son had never remembered to honor the Lar. The Lar kept the gold hidden until Euclio, the man's grandson, had a daughter who was ready for marriage, yet hadn't enough money for a dowry. Euclio, a dreadful miser, also neglected the Lar. But his daughter was of a more pious disposition, and had become pregnant by a man whose name she did not know. So the spirit sets in motion a complicated chain of events whereby Euclio finds the gold, but ultimately sees the error of his miserly ways and bestows it on his daughter for a dowry. Plautus describes the Lar Familiaris as a young, slender figure clad in high boots, short tunic, and a belted undergarment. Garlands adorn his head, and he is lithe, graceful and nimble.
- Federica Giacobello, Larari pompeiani. Iconografia e culto dei Lari in ambito domestico, LED Edizioni Universitarie, Milano, 2008, ISBN 978-88-7916-374-3