Suovetaurilia

The suovetaurilia or "suovitaurilia" was one of the most sacred and traditional rites of Roman religion: the sacrifice of a pig ("sus"), a sheep ("ovis") and a bull ("taurus") to the deity Mars to bless and purify land (Lustratio). 
Summary.
The ritual is preserved in Cato the Elder's "De Agri Cultura", "On Agriculture". The first step was to lead the three animals around the boundaries of the land to be blessed, pronouncing the following words:
"Manius" in this passage may be an obscure minor deity, related to the Manes, or may be the equivalent of English John Doe. Then, before the sacrifice is performed, the following prayer to Mars must be made:
The original Latin of this prayer is crudely metrical and incantatory; even in Old Latin, the prayer contains many rhetorical figures such as alliteration and liberal use of merisms and antithesis. It illustrates the sing-song, metrical, and poetic format of polytheistic prayers. Cakes of bread were sacrificed along with the three animals. At the moment the sacrifices were made, the landowner was to say:
If favourable omens as a response to the sacrifice were not forthcoming, the landowner was instructed to redo the sacrifice and offer a further prayer:
If only one or two of the omens expected after the three sacrifices failed to appear, the landowner was instructed to offer an additional swine, saying:
The nature of the expected omens is not given by Cato. The omens, however, were likely determined by the art of haruspicy, the examination of the entrails, and especially the livers, of sacrificed animals for divinatory signs. 
Both public and private "suovetaurilias" were performed in the Roman religion. Cato describes the ritual performed to purify, or "lustrate", a farm. A private rural "suovetaurilia" was sacrificed each May on the festival of "Ambarvalia", a festival that involved "walking around the fields." Public "suovetaurilias" were offered at certain state ceremonies, including agricultural festivals, the conclusion of a census, and to atone for any accidental ritual errors. Traditionally, "suovetaurilias" were performed at five year intervals: this period was called a "lustrum", and the purification sought by a "suovetaurilia" was called lustration.
If a temple were destroyed, the site of the temple must be purified by a "suovetaurilia" before a new temple could be reconstructed on the site. When the Capitolium was burnt as a result of a struggle for imperial succession in the year 69, a "suovetaurilia" was performed to reconsecrate the site. A public "suovetaurilia" was also offered to bless the army before a major military campaign. On Trajan's column, the emperor Trajan is depicted as offering a "suovetaurilia" to purify the Roman army. A suovetaurilia is shown on the right hand panel of The Bridgeness Slab. It was suggested that the sacrifice might have been made at the start of the building of the Antonine Wall.
Parallels.
Some religious rites similar to the Roman suovetaurilia were practiced by a few other Indo-European peoples, from Iberia to India. The Cabeço das Fráguas inscript (found in Portugal) describes a threefold sacrifice practiced by the Lusitanians, devoting a sheep, a pig and a bull to what may have been local gods. In the Indian "Sautramani", a ram, a bull and a goat were sacrificed to Indra Sutraman; in Iran ten thousand sheep, a thousand cattle and a hundred stallions were dedicated to Ardvi Sura Anahita. Similar to the above rituals is the Greek "trittoíai", the oldest known being described in the "Odyssey" and dedicated to Poseidon. The philosopher and historian Plutarch related in the "Lives Of The Noble Greeks And Romans" a story from the life of Pyrrhus about the sacrifice of a ram, a pig and a bull. The Umbrian Iguvine Tables also describe a sacrificial ritual related to the aforementioned rites. 