(note: automatic translation; please, allow few days to review it)
The usage of the coin arrived late in Rome in comparison to the rest of the Mediterranean, where the adoption of ancient coins in electrum (a natural alloy of silver and gold) in Lydia in Asia Minor toke place around the 600 B.C., the use of the coinage having then a quick diffusion in near Greece.
Before the introduction of ancient coins near the populations of central Italy, the commerce founded him on the exchange, using as mean of exchange the livestock (pecus), from which derives the Latin word pecunia used for pointing out the money. The first alternative to the exchange was I exchange him/it valued metal to weight; the availability of natural resources (mainly copper and pond, with the mineral one of scarce silver relatively) it made to prevail the use of leagues in bronze sottoforma of fused blocks of irregular form, varying dimensions and without any distinctive sign that you/they characterized them. From the Latin name of the "copper" or "bronze" (aes) it derives the indication of rough aes ("raw bronze, worked not") of this form of pre-coin, name then also used for the as the first Roman coin. Technically, in fact, the rough aes cannot be considered a coin yet since it misses a weight (and therefore a value) default and you mark that they identify the value of the object and the issuing authority that it guarantees the characteristics of it of it.
The rough aes was the mean of exchange used to a large extent of central Italy for hundreds of years, even if he/she introduced the drawback to have to be weighed for every exchange, since its value was tied up to its weight, as for all the ancient coins, but this was different apiece of these objects. To this drawback it was begun to presumably set remedy in republican epoch, realizing some aeses signatum ("marked bronze"), that is ingots of metal of form to regulate (usually rectangular) even if he/she anchors with a varying weight, that you/they brought tied signs some way to their characteristics or manufacturing.
Also the aes signatum was not able he/she anchors a coin to be considered, since he/she didn't introduce uniformity of weight and therefore of value.
As it regards the dating of the introduction of the bronze as mean of exchange it doesn't exist an uniformity of opinions. In his "Naturalis historia", Plinio makes to go up again the introduction of the aes signatum to Servio Tullio (578 a.Cs. - 535 a.Cs.), but many researchers put this evolution toward the IV century a.C., during the Roman Republic (509 a.Cs. - 44 a.Cs.).