The Lar, known also as the Lar familiaris, was the Roman household deity who protected the land that the family lived upon. The Lar was the center of the household cult, his shrine, known as a lararium was usually in one of the common rooms of the house, so the entire family and slaves could make offerings, always on the Kalends, Nones and Ides, as well as on special occasions such as banquets. It was only in the time of Augustus that the plural lares was used.
"Keeper of the Gate"
/Quoting from: Crapsey, Algernon Sidney. The Ways of the Gods. New York: The International Press, 1920. (Out of Print)/
The family as we know it today bears little of no relation to that ancient institution of which the Lar was the "Keeper of the Gate". In the early history of Rome, the title to the land was possession and use, because it was to a Roman the source of his life, its cultivation gave him occupation, upon the land he build his house and in the land he made his grave, therefore the land to the archaic man was sacred; for not only was it the home of the living, it was also the place of the dead, and it was the dead ancestors in their graves who really possessed the land and, as the Lares, were the "Keepers of the Gates".
Fear and reverence of the Lares
The belief of the ancient man in the ghosts of his fathers, with their unknown power to help and harm, was better than a title deed to secure each man in the possession of his land. Every family feared the Lares of every other family. The earth in those days was peopled with a host of spiritual beings — unseen, unheard, smiting with the pestilence, and killing with the plague. If any untoward accident befell a man, or sickness came to him after he had trespassed on his neighbor's land, then he, as well as his neighbor, ascribed his misfortune to the wrath of the Lar of that land. Thus each man had a wholesome fear of the ghosts of his neighbor. He was ready to fight his neighbor, whom he could see, but not his neighbor's ghosts, whom he could not see.
The temple to the Lares is first mentioned in connection with a series of prodigious events (106 BC):
Amiterni cum ex ancilla puer nasceretur, ave dixit. In agro Perusino et Romae locis aliquot lacte pluit. Inter multa fulmine icta Atellis digiti hominis quattuor tamquam ferro praecisi. Argentum signatum afflatu fulminis diffluxit. In agro Trebulano mulier nupta civi Romano fulmine icta nec exanimata. Fremitus caelestis auditus et pila caelo cadere visa. Sanguine pluit. Romae interdiu fax sublime volans conspecta. In aede Larum flamma a fastigio ad summum columen penetravit innoxia. Per Caepionem consulem senatorum et equitum iudicia communicata. Cetera in pace fuerunt. - Iulius Obsequens 41
And it was part of the original pomerium of the City:
Regum in eo ambitio vel gloria varie vulgata: sed initium condendi, et quod pomerium Romulus posuerit, noscere haud absurdum reor. igitur a foro boario, ubi aereum tauri simulacrum aspicimus, quia id genus animalium aratro subditur, sulcus designandi oppidi coeptus ut magnam Herculis aram amplecteretur; inde certis spatiis interiecti lapides per ima montis Palatini ad aram Consi, mox curias veteres, tum ad sacellum Larum, inde forum Romanum; forumque et Capitolium non a Romulo, sed a Tito Tatio additum urbi credidere. mox pro fortuna pomerium auctum. et quos tum Claudius terminos posuerit, facile cognitu et publicis actis perscriptum."
(There are various popular accounts of the ambitious and vainglorious efforts of our kings in this matter. Still, I think, it is interesting to know accurately the original plan of the precinct, as it was fixed by Romulus. From the ox market, where we see the brazen statue of a bull, because that animal is yoked to the plough, a furrow was drawn to mark out the town, so as to embrace the great altar of Hercules; then, at regular intervals, stones were placed along the foot of the Palatine hill to the altar of Consus, soon afterwards, to the old Courts, and then to the chapel of the Lares. The Roman forum and the Capitol were not, it was supposed, added to the city by Romulus, but by Titus Tatius. In time, the precinct was enlarged with the growth of Rome's fortunes. The boundaries now fixed by Claudius may be easily recognized, as they are specified in the public records.) - - Tacitus, Annals xii.24
Sacredness of private property
In the good old days every house was haunted and every field bewitched, and it was the haunt and the bewitchment that was the safety of the house and the land. Domestic religion was the keeper of domestic wealth and life. It was the fear of the Lares that gave sacredness to property and made theft and trespass not only a crime but a sacrilege.
This sacredness of property was religion in its origin. It existed for centuries before it gave rise to the civil laws that are now its security. Long before the reign of the law we had the reign of Lar. Each house-father, absolute lord and master of his own house and land, was under the protection of his Lar; the fear of them and the dread of them was upon all the country-round about. If his lands were seized by a stronger man than he, his Lar were expelled from the land, the graves of his ancestors violated, and he and his household were either killed or reduced to slavery.
This relation of the family to the land, and of the house-father to the family, classified ancient society as master and slave, patron and client, patrician and plebeian. With the institution of the family, there came into existence a class of out-family men and women: runaway slaves, prodigal sons, remnants of broken families; men and women without land, without Manes, without Lares, having no place at any family altar. Private property in land, the basic principle of the family, was the fruitful cause of poverty, with the wretchedness and degradation that always follow in its camp. That same poverty is today destroying the family and changing the face of civilization.
Private property in land has, in the course of time, passed out of the keeping of the family Lar into the care of the civil law; what man had once to do for himself society now does for him. The "Keepers of the Gates" were no longer the Lares but the lawyers.
Beard & North "Religions of Rome"