While the first use of glass is not exactly known, glass making as an ancient art has been around since the dawn of human civilization. Glass blowing, however, is thought to have developed in the era of Caesar, mid first century BC. Glass in the ancient world was considered a very valuable commodity available only to the extremely wealthy, and in small sizes for cosmetic, not practical purposes. With the invention of glass blowing, glass became generally available for inclusion in various public works and to the general population.
Like most technological advances in the Roman world, glass making did not originate from craftsmen in the Roman Empire, but many advances were made when the art form was incorporated within its borders. Of course, the establishment of any commodity, whether luxury or necessity, flourished with the Empire, as the population had the resources available to develop and use any existing technology. During the reign of Augustus glassmakers established themselves in Rome and other parts of Italy in abundance. At this point, forming glass would still be considered primitive by later techniques, such as the use of molds rather than free form blowing.
In ancient times molten glass was kept in a liquid state using a wood-burning furnace and the process must have been exhausting. Fortunately, thousands of examples of ancient glass art survive, but many have been removed from their original finds, making the determination of their historical context difficult. The ancients used glass much as we do in modern society, for windows, containers and artwork in many forms, and surviving samples paint a broad picture of the scope of glass used in Roman times. Unfortunately, no ancient sources exist describing the glass making process. Though there have been many advances, especially in mass production, the simple art of the ancient craftsmen would be very similar to the artisans of today, with the notable exception of available tools.
There aren't many known sites where glass was blown in a factory setting, but two in particular have been a great help to archaeology. Partial remains near Cologne, and in Phiadius in Greece dating from the 5th century BC, provide important clues. Not only does the existence of these glass factories provide insight into the production of glass but they also confirm the widespread use of glass throughout the ancient world. Syria, and eastern provinces in particular were a major source of moulded glass bowls and specialty products such as mosaic pieces. However, the existence of mosaics and other products throughout the Mediterranean proves that glass could and would be crafted in any part of the empire.