David McCullough in his book "The Path Between the Seas," wrote: The creation of a water passage across Panama was one of the supreme human achievements of all time, the culmination of a heroic dream of over four hundred years and of more than twenty years of phenomenal effort and sacrifice. The fifty miles between the oceans were among the hardest ever won by human effort and ingenuity, and no statistics on tonnage or tolls can begin to convey the grandeur of what was accomplished. Primarily the canal is an expression of that old and noble desire to bridge the divide, to bring people together. It is a work of civilization.

Why does the author say that the Panama Canal is a “work of civilization”?