Puma Punku, Koricancha, Ollantaytambo, Yuroc Rumi and in ancient Egypt metal clamps were used in their largest structures.
Evidence of the grooves and holes in which they were used can still be observed. At first archaeologists believed that clamps were brought to these grooves to be placed, but recent scans have revealed that metal was poured into these indentations, which means the builders had portable smelters. It is said that the metals used could only be melted at very high temperatures; temperatures the ancients (to our knowledge) were not capable of.
The Puma Punka brackets holes, when analyzed, showed platinum, a metal which only melts at 1753 C and aluminum, which supposedly was not discovered and produced in quantity until the 19th century.
One has to wonder why this technology as well as the incredible methods used to build these megalithic ruins became lost in the immediate centuries afterwards. A technology developed continues to fan out, but a less advanced civilization will lose the technology in time if they have not acquired the essentials.
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