have been mostly slaves, but throughout the Empire, slave farm labour was probably less important than other forms of dependent labour by people who were technically not enslaved. Textile and clothing production was a major source of employment. Both textiles and finished garments were traded among the peoples of the Empire, whose products were often named for them or a particular town, rather like a fashion "label". Better ready-to-wear was exported by businessmen (negotiatores or mercatores) who were often well-to-do residents of the production centres. Finished garments might be retailed by their sales agents, who travelled to potential customers, or by vestiarii, clothing dealers who were mostly freedmen; or they might be peddled by itinerant merchants. In Egypt, textile producers could run prosperous small businesses employing apprentices, free workers earning wages, and slaves. The fullers (fullones) and dye workers (coloratores) had their own guilds. Centonarii were guild workers who specialized in textile production and the recycling of old clothes into pieced goods. GDP and income distribution Economic historians vary in their calculations of the gross domestic product of the Roman economy during the Principate. In the sample years of 14, 100, and 150 AD, estimates of per capita GDP range from 166 to 380 HS. The GDP per capita of Italy is estimated as 40 to 66% higher than in the rest of the Empire, due to tax transfers from the provinces and the concentration of elite income in the heartland. In regard to Italy, "there can be little doubt that the lower classes of Pompeii, Herculaneum, and other provincial towns of the Roman Empire enjoyed a high standard of living not equaled again in Western Europe until the 19th century AD". In the Scheidel–Friesen economic model, the total annual income generated by the Empire is placed at nearly 20 billion HS, with about 5% extracted by central and local government. Households in the top 1.5% of income distribution captured about 20% of income. Another 20% went to about 10% of the population who can be characterized as a non-elite middle. The remaining "vast majority" produced more than half of the total income, but lived near subsistence. The elite were 1.2–1.7% and the middling "who enjoyed modest, comfortable levels of existence but not extreme wealth amounted to 6–12% (...) while the vast majority lived around subsistence". Architecture and engineering The chief Roman contributions to architecture were the arch, vault and