The extent to which the Incas did it is remarkable, but historically civil engineering had little to do with markets. The ancient Sumerians, Egyptians, Persians etc. pretty much built their infrastructure and monumental buildings with drafted, unpaid labor. The French monarchy, one of the most advanced states in the world, relied on the <i>corvée</i> to build roads up until 1789 [1]. The decisive turn in the situation took place in Holland around the 16th century, when Dutch cities discovered they could build canals and recoup costs by charging moderate usage fees. This system of financing civil engineering, adapted to e.g. turnpikes and later railroads, increasingly became widespread, and displaced earlier arrangements in Western countries during the 18th and 19th centuries. So what would be truly surprising is if the Incas <i>had</i> done it with money.<p>[1] <a href="http://en.wikipedia.org/wiki/Corvee#France" rel="nofollow">http://en.wikipedia.org/wiki/Corvee#France</a>