As the top-ranked city, Constantinople served as the 'golden key' between Europe and Asia and stood as the absolute economic engine of the ancient world. By the 10th century, it is estimated that customs duties alone accounted for over one-third of the Byzantine Empire's total budget. Interestingly, by monopolizing the trade of silk and spices, the city amassed wealth unimaginable to the rest of the Western world. Historians estimate that at its peak (circa the 8th century), Constantinople boasted a population of nearly 500,000, while contemporary London or Paris housed only a few thousand. This hundred-fold difference in population density solidified its position as not just a trading hub, but the world's primary center for logistics and finance for over a millennium.