From a macro economic perspective, wider per capita gap is not a sign of wealth, it is a symbol of an unhealthy economy. This is especially true when Urban Roman population probably didn't surpass 5% of the entire empire(and thats not even including the lowest of the classes which could not enjoy such facilities) while the slave population is at least twice that amount.
The 5% figure was the estimated rate of urbanization of Europe and China during the Middle Ages, according to this:
(however, I don't put much faith the accuracy of these estimates for China, while European estimates are better, as we have better data)
While the urban population of the Roman Empire surely was larger than 5% of the population of the entire empire. The city of Rome alone had 1.5-2% of the population of the entire empire, summing up with the other 4 major cities we get almost 5%, just with the cities numbering into hundreds of thousands. And there were many small cities in the empire, about 2,000 urban centers, Italy alone had 430 urban centers.
The Roman Empire was different from other pre-industrial empires in that it was an empire of cities around the mediterranean sea. It consisted of a network of cities, headed by the city of Rome. As result the Romans were a people of urban culture.
So what was the rate of urbanization of the Roman Empire? We don't know. We have rought estimates of the rate of urbanization of certain regions of the empire, according to the book City and Hinterland, Roman Italy had a rate of urbanization of 40% counting all the towns over 1,000 inhabitants, while Roman Egypt had a rate of urbanization between 25 to 35%, counting only the nome capitals. A more rigorous estimate puts the rate of urbanization at 43% at the North African island or Jerba, using field survey methods, and 14% of the Italian valley of Albegna, at the 1st century CE (the average is 28.5%). Those rates of urbanization are very high for pre-modern societies (the 40% rate of urbanization for Roman Italy is actually higher than any part of the world in the 18th century, including England and the Netherlands). In the book, Quantifying the Roman Economy, professor Los Cascio even though that these rates of urbanization were apparently too high to be true for a pre-industrial economy.
It would be theoretically possible for the Roman Empire to have a low rate of urbanization only if we assume that all the regions we have analized were exceptional, but how scientific is that? If all the evidence points out to a high rate of urbanization, why should we assume a low rate of urbanization? Overall, Classical Greece and the mediterranean provinces of the Early Roman Empire appear to have attained a rate of urbanization around 30%, counting only towns and cities over 5,000 inhabitants.
The rate of urbanization data suggests that the Roman economy was productive and efficient if compared to other pre-industrial economies. While by modern standards a rate of urbanization of circa 30% is the average for Africa. So we must understand that from modern standards, all pre-modern economies were very inneficient and living standards were oftem below what we consider today the minimum standards for subsistence.
Still the average size of escavated houses in Graeco-Roman cities from the 4th century BCE to the 1st century CE (from Olynthus, Priene in Classical Greece, to Dura Europus, in Seleucid Syria, to Pompeii and Herculaneum in Roman Italy), show that the average Classical house was larger than the average American house today! That's truly an impressive achievement. While huts and other signs of subsistence level living standards are rare for Greece in the 4th century BCE or Roman Italy in the 1st century CE (which represented respectively, the zenith periods of Greek and Roman civilizations). The median house size in 4th century BCE Greece was 240 square meters, in the first floor, Ian Morris estimates that about 50% of the houses had second floors, so the total median floor area was about 360 square meters, houses in Roman Italy were similar in size, but had more sophisticated decoration (on average, the houses in Pompeii and Herculaneum had 270 square meters and 8 rooms per house, and 60% of the houses in Pompeii and Herculaneum had decorated plastered walls, on average 5 decorated rooms per house). Still, Hadrill, the author of Houses and Society in Pompeii and Herculaneum, thinks that such luxurious living standards in Roman Italy were only possible thanks to the imperial extraction of income from the provinces.
The empire as a whole was poorer than Italy or classical Greece and there were great differences in the degree of development between the regions of the empire. For example, Britain was much poorer than Egypt and even wage data supports such theory: In Italy annual wages for unskilled workers were equivalent to about 3,000 kgs of wheat (data points ranges from 5,000 to 1,300 kg), in Egypt, wages were equivalent to 1,500 kg of wheat and in the recently conquered province of Dacia, annual wages were only equivalent to 800 kg of wheat. A family of 4 usually consumed 600-700 kg of wheat per year, so annual incomes of 800 kg of wheat were only enought to purchase the needed wheat plus some complementary foodstuffs. The average sizes of houses also show the same behavior, in Roman Italy houses had 270 square meters, in Roman Egpyt, 60 square meters and in Dacia most of the population still lived inside huts of 15-20 square meters. This huge difference can be undertood from the fact that in Dacia all income had to be spent on food, while in Italy, since there weren't many different goods beyond food and housing, people spent their substantial income above subsistence on housing.
I also advice to not use such adjectives as "unhealthy economy", to a polity that existed for 500 years, such broad characterizations don't make much sense. All the data I have posted here refers to the conditions of the Early Roman Empire (mostly from Augustus to Trajan). The Late Roman Empire was much less urbanized and developed than the Early Roman Empire, all archeological data suggests that population density decreased in all regions of the empire, while the western regions suffered the greatest decline, and the volume of trade and the production of commodities also show a decline in the eastern regions. The economy of the empire became less market oriented and less of a pan-mediterranean integrated economic system to a system of self sufficient villas. The peasants working in those villas became tied to the land and these are ultimately the origins of serfdom.
The 5% figure for the rate of urbanizaion in the Roman Empire may apply to the Empire around 400 CE, at the time of the barbarian invasions, when the clasiscal Graeco-Roman civilization was already dead inside.
By the standards of Marxist history, the Roman economy was formally labeled as the slave mode of production while the Han economy was already in the feudal mode of production(based on land privitization and free peasants) and hence the later is actually in a further stage of development in history(there are five stages in Marxist history) in terms of class structure. However, this standard doesn't really reflect wealth and it is nothing more than a theory.
Marxism is not only a theory, it is pretty much a dead theory, since it's economic foundations were decisively refuted already in the 1890's by Böhn-Bawerk. Why Marxism persists? Well, because Marxism is really a religion among some social scientists. The mechanical model where society progresses from slavery, to serfdom, to capitalism to socialism is ridiculous when one thinks about it. It is also based on western history, from the ancients to the modern times, but western history is not a history of constant progress, but of periods of progress, like the period from 800 BCE to 100 CE, and periods of decline and collapse, like from 100 CE to 700 CE. We can even consider the civilization of the ancient Graeco-Romans to be a distinct civilization from modern European civilization. Modern Western civilization emerged from the ruins of the ancients.
Slavery strictu sensu is the state were persons can be brought and sold as private property in the slave market. It is actually a quite sophisticated form of unfree labor. Serfdom consists of laborers tied to the land, hence there is no market for serfs and the serfs are de facto slaves of the manor, but the manor doesn't buy and sell them. So it can be actually understood as a more primitive form of slavery. A form of fixed slavery. It is less effiecient than slavery because slaves tend to be allocated where they are most productive, while serfs are tied to their occupation.
Also, in medieval europe the vast majority of the population consisted of serfs and in the Roman Empire only a minority of the population of the roman empire consisted of slaves. One has to take that into account as well. If we assume that serfdom is more advanced than slavery but less advanced tham free labor, a society with 80% free laborers and 20% slaves is not necessarily less advanced than a society with 90% serfs and 10% free laborers.
None of these are really beneficial to the population at large, urbanized or not. But I don't believe technology needs to be measured based on how it was available to the general public.
These facts are a rought indicator of the engineering capabilities of a society. They don't mean anything directly, like the fact that the US put the men on the moon while Nigeria didn't doest necessarily mean that the US has better living standards than Nigeria. Japan and Germany don't have living standards significantly inferior to the USA's, but they didn't put the men on the moon.
Overall, Roman civil engineering was more advanced than 18th century Europe and the mediterranean parts of the Early Roman Empire were also more urbanized than 18th century Europe. Archeological evidence also shows that living standards in the Early Roman Empire were probably better than 18th century Europe, at least in Italy and the Aegean regions.
While I am not very much aquainted with the economic history of China (in fact, I don't think there has been much serious research about the economic history of China, serious study of Western Ancient Economic history, using archeological and quantitative evidence, has just started), the evidence that I have indicate that Han China was less sophisticated in terms of economic development than Classical Greece and the mediterranean provinces of the Early Roman Empire. Perhaps Song China was more comparable, as they had already developed a large canal network, that could mimic the beneficial properties of the mediterranean sea. The basis for the social development achieved by the classicals was the mediterranean sea, which allowed the cheap transportation of goods and therefore allowed a unified pan-mediterranean economy (exemplified by the fact that Athens imported most of their food, though their port, and that Roman Carthage had it's buildings made of bricks imported from Italy, hundreds of miles away), that allowed the division of labor of the working populations of the entire mediterranean basin.
An interesting set of papers in the economy of classical Greece has been recently presented in Athens in september 2010:Economy of classical Greece
Edited by Guaporense, 04 July 2011 - 02:25 PM.