Gaius, Institutes, Book II. Ad Dig. 1,8,1 pr.Windscheid: Lehrbuch des Pandektenrechts, 7. Aufl. 1891, Bd. I, § 146, Note 16.The principal division of Things is under two heads: for some of them belong to Divine and some to human law. Those which come under Divine law are, for instance, sacred and religious things. Sacred things are, for example, walls and gates, which, to a certain extent, are under Divine law. For what is subject to Divine law is not the property of anyone, and that indeed which belongs to human law is, for the most part, the property of someone, nevertheless, it may belong to none, for things belonging to an estate until an heir appears, are not the property of anyone. Again, those things that are under human law are either public or private. Those which are public are held to be the property of no one, and are considered to belong to the entire community, and those which are private belong to individuals. 1Moreover, some things are corporeal, and some are incorporeal. Those are corporeal which are tangible, as for instance land, slaves, clothing, gold, silver, as well as innumerable other articles. Those are incorporeal which cannot be touched as an usufruct, and obligations, in whatever way contracted. It does not matter if corporeal things are included in an estate, for the crops taken from land are corporeal, and whatever is owing to us through the obligation of another, is for the most part corporeal, as land, slaves, money; still, the right of succession, the right of use and enjoyment, and the right based upon an obligation are all incorporeal. To the same class belong all the rights of urban and rustic estates, which are designated as servitudes.

Gaius, Institutes, Book II. If we make inquiry as to whether a will is valid, we should first ascertain whether he who made it had the right to do so, and then, if he had, we should ascertain whether it was drawn up in accordance with the rules of the Civil Law.

Gaius, Institutes, Book II. Those also are included among posthumous children who, by succeeding to the place of proper heirs, through their birth become the lawful heirs of their parents. For instance, if I have a son, and a grandson or a granddaughter born to him, all under my control, as the son takes precedence by a degree in the succession, he alone has the right of a direct heir, even though the grandson and granddaughter, who are his children, are also under my control. If, however, my son should die during my lifetime, or, for any reason whatsoever, should be released from my control, the said grandson and granddaughter will take his place in the succession, and in that way their rights as direct heirs will be acquired, as it were by birth, but my testament will not be broken in this way, just as if I should appoint or disinherit my son as my heir; nor can I legally make a will in such a way that it will become necessary for me to appoint as heir, or disinherit my grandson or my granddaughter, unless my son having died during my lifetime, and my grandson or granddaughter having taken his place in the succession, should break the will, just as is done by birth; and this the Lex Julia Velleia provided for.

The Same, Institutes, Book II. Property is acquired for us not only by ourselves, but also by those whom we have in our power; as, for instance, by slaves in whom we have the usufruct, and also by freemen and slaves belonging to others of whom we have possession in good faith. Let us consider each of these cases in detail. 1Hence, anything which our slaves obtain by delivery, or which they stipulate for, or acquire in any other way whatsoever, is acquired by us; for he who is in the power of another can have nothing of his own. Therefore, if our slave is appointed an heir, he cannot enter upon the estate unless by our order, and if we order him to do so, the estate is acquired by us, just as if we ourselves had been appointed heirs. In conformity with this principle, a legacy also is acquired by us through our slave. 2Moreover, not only is ownership acquired for us by those whom we have under our control, but possession is also; for when they obtain possession of the property of anyone, we, ourselves, are considered to possess it; hence ownership is also acquired for us by long-continued possession. 3With reference to those slaves in whom we have only the usufruct, it has been decided that when they acquire anything through the use of our property, or by their own labor, it is acquired by us. If, however, they obtain anything by any other means, it will belong to him in whom the ownership of them is vested. Therefore, if a slave of this kind is appointed an heir, or if anything is bequeathed or given to him, it will not be acquired by me but for the owner of the property. 4The same rule which has been adopted with reference to an usufructuary is also applicable to one who is possessed by us in good faith, whether he is free, or a slave belonging to another; and is available in the case of a bona fide possessor. Hence, whatever is acquired in any other way than the two above mentioned will either belong to the person himself if he is free, or to his master if he is a slave. 5Still, where a bona fide possessor obtains a slave by usucaption, for the reason that, under these circumstances, he becomes his owner, he can acquire property through him in every way. An usufructuary, however, cannot acquire a slave by usucaption; first, because he does not actually possess him, but merely has the right of using and enjoying him; second, because he knows that the slave belongs to another.

The Same, Institutes, Book II. He does not commit a theft, for a theft cannot be committed without the intention of stealing. 1Anyone can also obtain possession of the land of another without violence, where it has become vacant through the neglect of the owner, or where the latter has died without leaving an heir, or has been absent for a long time.