EDITED: by Ariel Turpin on 12/14/2011 Checked for formatting, spelling, grammar, and plagiarism.
The development of coinage in Ancient Roman civilization came as a result of its place on the trade routes between the Greek colonies in Southern Italy, and Etruscan city-states to the north of Rome. It was not until the reign of the Etruscan king Servius Tullius (r. 578 - 535 BCE) that history records the first minting of coins in Rome. This early coin was stamped with the image of cattle (pecus) from which derived the Latin word for money (pecunia). Minting coins meant that Romans could slowly replace the heavy bronze ingots, such as the Aes Rude(Rough Bronze) and the Aes Signatum(stamped bronze) which had been the traditional currency of Rome from the early 8th century BCE. As Rome expanded its reach across the Mediterranean world, contact with new cultures and the discovery of new mineral resources meant that coins of copper, silver, and gold could be minted. 
GENERAL COIN TYPES AND DENOMINATIONS
The earliest Roman coins were cast bronze based on the As (plural- Asses). The standard As originally weighed 1 pound, which could then be divided into 12 ounces (Latin - unciae). Denominations of these early coins, based on the amount of material it contained, were represented by raised dots. For example, a coin containing 4 ounces of material (or 1/3 of a 12 ounce As) would be represented by four raised dots. Due to the Augustan monetary reforms, the As and the Quadrans denomination which had been bronze since their inception, were changed to copper.
The availability of silver in the late 3rd century BCE made it more popular as a coin material. An early silver coin was the quadrigatus, so named for the image of a quadriga (four-horse chariot). It was introduced around 269BCE. Further standardization of the monetary system eventually led to the use of the denarius (pl. denarii) in 211 BCE as the principle Roman coin. In the mid-Republic period the Denarius had a value of 10 Asses. Two denominations of the denarius were the Victoriatus(valued 5 Asses) and the Sestertius(valued 2.5 Asses). Augustus also targeted the Sestertius during his reforms. He changed the coin's composition from bronze to brass. By the time of Constantine in the early 4th century CE, the denarius was no longer in use. It had been replaced in the 3rdcentury CE by the short-lived double denarius or antoninianus, and later by the follis or silvered-bronze coin introduced during the reign of Diocletian in the late 3rd century CE. Of all Roman coins, the follis (pl. folles) is the hardest to assign value, due to the rapidly changing economy during the later Roman period. Folles, as opposed to other coins, are categorized not by weight of material, but by the coins' diameter.
Gold coins were rare during the Roman Republic. The aureus (from Latin aurum-"gold") was not a regularly minted coin until the time of Julius Caesar. The aureus had a value of 25 denarii. As with the denarius, the aureus did not survive into the Late Empire. It was replaced by a coin known as the Solidus, said to have a value of 1000 denarii due to the debasement of the denarius' value by that time.
- Dictionary of Greek and Roman Antiquities by William Smith, First American Edition, Harper & Brothers, 1843, http://books.google.com/books?id=9e8rAAAAYAAJ&pg=PA29&lpg=PA29&dq=aes+grave+brass+or+bronze&source=bl&ots=E325po7iMA&sig=ALVTX4dmxASSzmrXQxj5v08u_pA&hl=en&ei=b27lTuHfA4Te0QGit8nfBQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDMQ6AEwAQ#v=onepage&q=aes%20grave%20brass%20or%20bronze&f=false
- Carausius and Allectus: the British usurpers by P.J. Casey, Yale University Press, 1995, http://books.google.com/books?id=Le5cjYt4ER0C&pg=PA86&lpg=PA86&dq=aureus+1000+denarii&source=bl&ots=tathFyg7Au&sig=HC-GapGcya8n3eM-6BXbY1wOKHU&hl=en&ei=u0vmTrykNorq0QHh7cHiBQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CC0Q6AEwAg#v=onepage&q=aureus%201000%20denarii&f=false