Elsewhere (in Roman marriage) it was discussed that persons in Rome were either sui iuris (i.e. not subject to the patriapotestas or power of a paterfamilias), or alieni iuris (subject to another’s patriapotestas). The power was acquired in various ways by a paterfamilias, e.g. children born from a Roman marriage automatically fell under the power of the paterfamilias, slaves purchased and other persons in bondage (free persons under certain circumstances fell under the power of the paterfamilias, even if they were not family, see later), the wife married cum manu (under the hand / power of her husband), or people who were adopted into a family, were generally speaking all regarded as alieni iuris.
At this juncture it must be emphasized that the notion of family in Rome was a much more extended concept than our modern one. Family consisted of the entire patrimony of the paterfamilias, and therefore included everybody and everything the paterfamilias was responsible for, therefore also all property, animate and inanimate. For this reason, it was necessary that the persona of the paterfamilas continue in perpetuity, in order to allow always for someone who could take the necessary responsibility for all the people and property that fell within the familia. In cases where a paterfamilias did not have a suus heres (legitimate (male) heir), it would be necessary to adopt someone who could step into the shoes of the paterfamilias, so to speak.
Two forms of adoption were known to the Romans, both of which served separate functions, and followed separate forms, although the effect was ultimately the same. Adrogatio was used in order to adopt someone sui iuris into the potestas the adopting paterfamilias (in which case the adopted person lost his status and became ailieni iuris), while adoptio was used to adopt into the adopting paterfamilias’ potestas someone already (or still) alieni iuris. Of the two forms, adrogatio was the older and stricter form, initially used to specifically provide for situations where there was no suus heres who could continue the persona of the paterfamilias, and also the control of the familia.
Adrogatio effectively entailed the extinction of one familia (constituted by the adoptive person being sui iuris) in order to enable another to continue, and for this reason it had a distinctly public character, while adoptio was a much more private law orientated issue, concerning as it did someone already (or still) alieni iuris. Indeed, Thomas1 states that adoptio originally served an economic function, redistributing labour in early times when slaves were a scarce commodity.
Each familia was also possessed of a sacra, a religious observance of the household gods, the lares and penates, being the gods and the spirits of the forefathers of the particular familia. Necessarily, as we have stated, because adrogatio entailed the extinction of the familia of the adrogandus (the person being adopted by way of adrogatio), the sacra of his familia would not continue. The result was that pontifex maximus (the supreme pontiff) became involved in order to ascertain the desirability (or not, as the case may be), of the adrogation, in order to ensure that it was both legal and justifiable under the circumstances. The matter was then referred to one of the popular assemblies, the comitia calata, which ratified certain business of the pontifex maximus. It must be borne in mind that the adrogandus was sui iuris, and by extension necessarily a paterfamilias, therefore a member of the assembly itself,2 and the assembly naturally had an interest in matters which gave rise to someone's loss of the right to participate in that assembly. Once the formal procedures had been completed, the legal construction placed on the adrogatio was that the adrogandus’ potestas had been terminated by order of the assembly, and the adrogandus then formally accepted the sacra of the familia of the adrogator (the adrogating paterfamilias). Obviously, all persons and property of the adrogandus now fell under the potestas of the adrogator as their new paterfamilias.
Gaius tells us3 that adrogatio could only be performed at Rome, as this is where the comitia calata assembled. This only happened twice annually, 24 March and 24 May. Under the empire, however, the emperor issued rescripts of adrogation on applications received from the outlying provinces.
It is generally accepted that adoptio is of later origin than adrogatio. The lex duodecim tabularum (law of the twelve tables) provided that a pater could free a son from his manus by selling him three times. Adoptio initially consisted simply of selling the son three times to another, which would transfer the son to the potestas of the purchaser as a free person, Roman citizens not being capable of being sold into slavery within Rome itself.4 Later a more formal procedure became the norm, by the pater mancipating (freeing from his potestas by way of a formal process called mancipatio) the son to the adoptor (adoptive pater) three times (simulating the ancient sale). The matter was then finalised before the praetor who simply upheld the adopting father’s claim that the child is his son, while the previous father made no defence to the claim.
See also Roman marriage and Roman names.
1 A Textbook of Roman Law 1976, 437.
2 Which explains why women and children (persons under the age of puberty) could not be adopted by way of adrogatio, not having membership of the comitia.
3 Institutes I:100.
4 Only if the son was sold trans Tiberim (on the other side of the river Tiber) was he sold into slavery.