Real contracts were the oldest type of contracts in the Roman law. Eventually there were several types of contracts in this category: loan for consumption (mutuum), deposit (depositum), loan for use (commodatum) and pledge (pignus). Initially there was only the loan for consumption which emerged from even older nexum.
Nexum (debt bondage contract) is considered to be the prototype of loan in the Roman law. It was a type of ceremonial legal action carried out per aes et libram (with the use of bronze and scales) in the presence of witnesses and as such it was available only for citizens. In case of not returning the borrowed sum, the borrower could be turned into a slave or even killed. As a consequence of social protests this institution was abolished by lex Poetelia Papiria passed close to the end of 3rd century BCE (the specific date is uncertain, historical sources vary in regard to this topic).
Mutuum as the successor of nexum prohibited killing and selling the insolvent debtor into slavery. The name of this legal action comes from the verb mutare which means to exchange. Any fungible things specified in regard to their type could be a subject of a loan, therefore the borrower was supposed to return things which were identical with the borrowed things but not the borrowed things themselves. It was a one-sided obligation stricti iuris (strict law).
There were many types of loan. One of the types was a loan for an athlete intended for his training and costs of living. In this case the obligation to pay the loan back arose only if the athlete won a competition and received a prize. Another type was a sea loan. The obligation to pay back arose only if the ship managed to reach the destination harbour with its load. The risk incurred by the money lenders was balanced by the acceptance of very high interests. The creditors secured themselves by using their right to choose the shipping routes and getting a pledge on the transported goods. The sea loan was often used as an insurance – the borrower was secured against e.g. unfavourable consequences of a storm or an encounter with pirates.
The loan was in principle free of charge but the interest could be added separately with the right stipulation. Friendly loans were used to enter a contract with relatives without the interest stipulation. Contractus mohatrae in turn had a form similar to the contemporary commission – the debtor received a non-consumable thing and the right to sell it and keep the money. Another type of loan was the pactum de mutuo dando – the promise to give a loan in the future. Mandatum qualificatum was an order for the other party, usually a bank, to give a loan to a third party.
A loan could be entered also by a transfer (delegatio). In order for such a contract to become valid the creditor (the transfering one– delegans) had to order the debtor (the transferred one – delegatus) to pass the sum of the debt to a third party (the receiving one – delegatarius). At the same time he demanded the receiver to accept the money from his debtor. This way the relation of a loan emerged between the creditor and the receiver of the transfer.
The lender could use different means in order to defend himself in court. If a specific sum of money was the subject of the loan, then he could use actio certae creditae pecuniae. If however things specified with respect to their type were the subject of the loan, actio tritica was used. It was also possible to use actio ex stipulatiu in order to secure interest based on the stipulation.