According to Rohl, "There is little evidence of kingship and its rituals very much before the beginning of the 1st Dynasty; no signs of the gradual development of metal working, art, monumental architecture and writing—the defining criteria of early civilisation. Much of what we know about the pharaohs and their complex culture seems to come into existence in a flash of inspiration." Rohl believes the catalyst for this sudden development was the influx of a Mesopotamian "foreign elite" who made their way to Egypt by sailing around the coastline of the Arabian Peninsula into the Red Sea ultimately dragging their boats across the desert to the Nile. Rohl notes numerous pre-dynastic rock carvings found in several locations from Wadi Abbad to Abydos which is suggested depict large Mesopotamian style boats with crews of up to 75, some of which appear being pulled across land. Rohl believes the most dramatic evidence to support this theory is the sudden introduction of distinctly Mesopotamian "niched-facade", also known as "palace facade", architecture found in several early Dynastic sites, most notably the large 1st Dynasty mastabas at Saqqara. A depiction of a building using this kind of architecture is also an integral part of the serekh, the early Egyptian seal of kingship, and is found before the 1st Dynasty as well in the Naqada III, or "Dynasty 0" period. He says, "It is highly improbable that such specialized building techniques were independently invented in two widely separated regions at the same historical period without cultural transmission.