The knowledge needed to evaluate certain of these ancient artifacts was not available until very recently. Even today there may be numerous articles that we will not understand until we further develop our own technology. We cannot fathom technology that is unknown to us, and we seldom consider things that seem impossible to us. Petrie, though knowledgeable in engineering and surveying, could not be expected to know anything about ultrasonic machining; hence his amazement at the machining abilities of the ancient Egyptians. Even if he had been aware of this technology, the intellectual climate of his time may have precluded his considering the possibility that these methods were known to the ancient Egyptians. Quite simply, the greatest barrier to our understanding may not necessarily be knowledge. It may be attitude. The Giza Power Plant: Technologies of Ancient Egypt