The Arch is one of the amazing twentieth century creations that resulted from advances in engineering and architectual innovators. Outweighing 7400 elephants and topping any other U.S. monument, the structure is a visionary statement both recalling the fervor of settlers who went into the unknown determined to make their fortune and answer Merriweather Lewis's call and perhaps foretelling other great migrations yet to come.
The visitor area also documents the hard reality of America's dishonorable treatment of the native American tribes displaced by the colonization of the West. Far too much was lost in the haste to justify expansion for power and profit ... yet across the river, there are remains of a city that collapsed before the Europeans arrived.
The story of the great mound city of Cahokia is one of unmanaged growth. Bolstered by the region's bountiful corn crops, the hierarchical society bent its efforts to building elevated dwelling places for the elite. When the city grew beyond the land's ability to support the population, disease and famine brought down the City of the Sun. The common granaries that had stabilized the city's economy when central authority held sway were replaced by family or clan-held stores, the city's population faded away. The largest mound temple in the Americas and one of the most complex astronomical observatories fell into ruin.
The civilization that built the city on the other side of the river might look for some lessons in that.
We spent a while examining Cahokia's Woodhenge, the city's astronomical observatory, and speculating on the designers' approach. Their use of red cedar sighting poles instead of stones gave them much more design flexibility; holes for several overlapping rings in the same area have been found, indicating that more than one observation grid was built.
Perhaps the relative ease in relocating the poles saved some past astronomer's career when these costly prediction systems failed to correctly predict auspicious events? It's a minor configuration issue, we've fixed it in the newest release ....
One curiosity we managed to resolve in part was the number of poles used to mark out the sighting directions.The builders of the best preserved (most successful?) circle at Cahokia divided the arc into 48 segments. Why?
Another visitors pointed out that unlike us, Cahokia's astronomers appeared to work more closely with the natural world than the pure numerical shadows. They had four key data points affecting their crop management planning: the two equinoxes, and the summer and winter solstices. Perhaps one of them recognized that relative to a sight line connecting the spring and fall equinoxes, the sight lines solstices above and below the fall equinox formed equal angles -- in our measurements, almost exactly thirty degrees above and below at Cahokia's latitude.
Setting these poles to match the observed positions of the sun formed the baselines they needed to support agriculture, and repeating that pattern around the circle would give 12 widely spaced poles. Dividing each of these larger segments into four equal parts, Barbara noted, would result in a very practical total of 48 poles.
Since more than one pole circle was built, though, suggests this practical solution was reached by trial and error. We can only imagine the foreman's reaction when the scholars came to him requiring the digging of yet another series of 48 carefully spaced holes deep enough to hold the red cedar poles upright.
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