Ver sacrum ("sacred spring") is a religious practice of ancient Italic peoples, especially the Sabelli (or Sabini) and their offshoot Samnites, concerning the dedication of colonies. It was of special interest to Georges Dumézil, according to whom the ver sacrum perpetuated prehistoric migration practices of Indo-Europeans to the end of the Iron Age and into the beginnings of history, when stable sedentary dwelling conditions had already become general.

The practice consisted of a vow (votum) dedicating to the god Mars all offspring (livestock and/or human) born in the following spring. Among the Sabines, this was the period from March 1 to April 30.

The practice is related to that of devotio in Roman religion. It was customary to resort to it at times of particular danger or strife for the community. Some scholars believe that in earlier times devoted or vowed children were actually sacrificed, but later expulsion was substituted. Dionysius of Halicarnassus states the practice of child sacrifice was one of the causes that brought about the fall of the Pelasgians in Italy.

The human children who had been devoted were required to leave the community in early adulthood, at 20 or 21 years of age. They were entrusted to a god for protection, and led to the border with a veiled face. Often they were led by an animal under the auspices of the god. As a group, the youth were called sacrani and were supposed to enjoy the protection of Mars until they had reached their destination, expelled the inhabitants or forced them into submission, and founded their own settlement.

The tradition is recorded by Festus, Livy, Strabo, Sisenna, Servius, Varro, and Dionysius of Halicarnassus.

Guide animals that led the group sometimes became the eponyms of the new community. These included the wolf (hirpus), after which the Hirpini of Campania were supposed to have been named; the woodpecker (picus), which gave its name to the Picentes who settled present-day Marche (hence the green woodpecker as the symbol of the region); the vulture (vultur) of the Vultures; and the horse (equus) of the Aequi or Aequicolae in Latium. The Samnites were led by an ox (bos), after which was named their capital Bovianum, founded upon the hill on which the ox had stopped. The Mamertini of Sicily received their name directly from the god Mars.

Guide animals from the ver sacrum and their legends may explain the use of animal insignia by the Roman army. Gaius Marius was the first to adopt the eagle in all the signa militaria; previously the eagle had been the first and highest of the signa. Others in use were the wolf, the Minotaur, the horse and the boar. Andreas Alföldi has linked each animal with a Roman god, starting with the eagle and Jupiter and ending with the boar of Quirinus: thus the wolf would be related to Mars, the Minotaur to Liber and the horse to Neptune.

Dumézil emphasizes the affinity of Indo-Iranian human and warrior gods with animal forms: among the Iranian god of victory V(e)r(e)thragna's incarnations, seven are of animal form, including the bull, horse, boar and hawk, each of which is associated at one time or another with a ver sacrum and Roman army insignia.