The contract of purchase and sale is complete immediately the price is agreed upon, and even before the price or as much as any earnest is paid: for earnest is merely evidence of the completion of the contract. In respect of sales unattested by any written evidence this is a reasonable rule, and so far as they are concerned we have made no innovations. By one of our constitutions, however, we have enacted, that no sale effected by an agreement in writing shall be good or binding, unless that agreement is written by the contracting parties themselves, or, if written by some one else, is at least signed by them, or finally, if written by a notary, is duly drawn by him and executed by the parties. So long as any of these requirements is unsatisfied, there is room to retract, and either purchaser or vendor may withdraw from the agreement with impunity—provided, that is to say, that no earnest has been given. Where earnest has been given, and either party refuses to perform the contract, that party, whether the agreement be in writing or not, if purchaser forfeits what he has given, and if vendor is compelled to restore double of what he has received, even though there has been no express agreement in the matter of earnest.

1 It is necessary that the price should be settled, for without a price there can be no purchase and sale, and it ought to be a fixed and certain price. For instance, where the parties agreed that the thing should be sold at a price to be subsequently fixed by Titius, the older jurists doubted much whether this was a valid contract of sale or not. The doubt has been settled in the following way by our decision; if the third person named actually fixes the price, it must certainly be paid, as settled by him, and the thing must be delivered, in order to give effect to the sale; the purchaser (if not fairly treated) suing by the action on purchase, and the vendor by the action on sale. But if the third person named will not or cannot fix the price, the sale will be void, because no price has been settled. This rule, which we have adopted with regard to sales, may reasonably be extended also to contracts of hire.

2 The price, too, should be in money; for it used to be much disputed whether anything else, such as a slave, a piece of land, or a robe, could be treated as a price. Sabinus and Cassius held the affirmative, explaining thus the common theory that exchange is a species, and the oldest species, of purchase and sale; and in their support they quoted the lines of Homer, who says in a certain passage that the army of the Greeks procured themselves wine by giving other things in exchange, the actual words being as follow: 'then the longhaired Greeks bought themselves wine, some with bronze, some with shining iron, some with hides, some with live oxen, some with slaves.' The other school maintained the negative, and distinguished between exchange on the one hand, and purchase and sale on the other: for if an exchange were the same thing as a sale, it would be impossible to determine which is the thing sold, and which is the price, and both things cannot be regarded in each of these characters. The opinion, however, of Proculus, who affirmed that exchange was a species of contract apart by itself, and distinct from sale, has deservedly prevailed, as it is confirmed by other lines from Homer, and by still more cogent reasons, and this has been admitted by preceding Emperors, and is fully stated in our Digest.

3 As soon as the contract of sale is concluded—that is, as we have said, as soon as the price is agreed upon, if the contract is not in writing—the thing sold is immediately at the risk of the purchaser, even though it has not yet been delivered to him. Accordingly, if a slave dies, or is injured in any part of his body, or if a house is either totally or partially burnt down, or if a piece of land is wholly or partially swept away by a river flood, or is reduced in acreage by an inundation, or made of less value by a storm blowing down some of its trees, the loss falls on the purchaser, who must pay the price even though he has not got what he purchased. The vendor is not responsible and does not suffer for anything not due to any design or fault of his own. If, however, after the purchase of a piece of land, it receives an increase by alluvion, it is the purchaser who profits thereby: for the profit ought to belong to him who also bears the risk. And if a slave who has been sold runs away, or is stolen, without any design or fault of the vendor, one should look to see whether the latter expressly undertook to keep him safely until delivery was made; for, if he did this, the loss falls upon him, though otherwise he incurs no liability: and this is a rule which applies to all animals and other objects whatsoever. The vendor, however, will be bound to transfer to the purchaser all his rights of action for the recovery of the object or damages, for, not having yet delivered it to the purchaser, he still remains its owner, and the same holds good of the penal actions on theft and on unlawful damage.

4 A sale may be made conditionally as well as absolutely. The following is an example of a conditional sale: 'If Stichus meets with your approval within a certain time, he shall be purchased by you for so many aurei.'

5 If a man buys a piece of land which is sacred, religious, or public, such as a forum or basilica, knowing it to be such, the purchase is void. But if the vendor has fraudulently induced him to believe that what he was buying was not sacred, or was private property, as he cannot legally have what he contracted for, he can bring the action on purchase to recover damages for what he has lost by the fraud; and the same rule applies to the purchase of a free man represented by the vendor to be a slave.