Petra "Lost City" of Jordan

The monastery at Petra, Jordan. There is a person in the doorway if you look really close, which shows the massive size of the construction (National Geographic, 2015).

The lost city of Petra! Sounds like something out of an Indiana Jones movie, which is funny since it was a film location for "Indiana Jones and the Last Crusade". Apart from the tourist destination and being a prime location for archaeological movies, Petra is fascinating for its water management techniques. The clever civilisation that lived in Petra and created all this were the Nabataeans. At their peak, the population was around 30,000 people which are a lot to cram into an arid city. 

Geology of the Area

The landscape in Petra, looks like a sea of yellow/orange and brown and made up of clay rocks and dust. The reason for the different colours is the composition. The oldest sandstone consists of coarse to medium grained quartz class, with an iron- and manganese-rich matrix. Below this layer of sandstone is a pre-Cambrian granite with gneiss and schists (Geotimes, 2004). The material exposed at the surface is primarily made up of different layers of sedimentary rocks that have been deposited throughout time. These layers are evident throughout the city as well as adjacent areas. The sandstones display old sand dune structures as well as cross-bedding and they have formed a steep, impressive canyon that leads you to the entrance of Petra, rather dramatically. According to (Geotimes, 2004) geologists have identifies the system as a braided river stream complex. There is then a friable, white sedimentary deposit on top of that and a limestone layer caps the high peaks of the region (Geotimes, 2004). The intricate water system of Petra helped buffer against erosion whereas surrounding the city wind and stream erosion deposits from the Holocene are evident (Geotimes, 2004).  
Petra sits on the western edge of the Arabian Plate to the south-east of the Dead Sea which can be seen in figure 1. There is a transform fault segment in the Dead Sea rift zone which the sandstone layers extend towards. Records show that there have been at least 20 major seismic events in the greater region. This is also evident in the city as there are fallen stone columns that line the main streets which relate to the earthquakes and aftershocks that overwhelmed the city in 363AD (Geotimes, 2004). The earthquake wrecked havoc in all areas to do with the city. Their water system crumbled due to displacement and movement caused by the fault. This lead to the surrounding sandstone being once again susceptible to weathering erosion. The flooding that created the canyon was a serious threat to the city at this time. Unfortunately, the shops that one lined the town are now filled with flood deposits, which tells you all you need to know (Geotimes, 2004). 

Figure 1: Google image of Petra in relation to the Red and the Dead Sea

Hydrology In Petra 

Throughout the city, there are a series of cisterns that held every drop of water that was rained down on them as well as water carried into the city by their "aqueducts" and pipes. I say aqueducts in quotation marks as they aren't the same as what we automatically think of like the Roman aqueduct bridges. These were channels dug into the side of hills in a downward gradient so the water flows down naturally, shown in figure 2. In some parts, there were covers over the channels to protect the water. The Nabataeans also created clay pipes that are tapered at the ends, something we have only figured out 200 years ago (Nabataea, 16/10/16). These pipes are a major advancement in their civilisation and can be seen in figure 3. 

Figure 2: Petra aqueducts dug into the side of the canyon walls.

(Wikimedia Commons, 2005)

Figure 3: Clay pipe with a tapered end

(Nabataea, 16/10/16)

By the sounds of it, Petra was a sprawling metropolis that had water irrigation for gardens and an advanced water system that allowed for a large population to survive in an arid climate. The softer rock in the mountains allowed for the Nabataeans to carve out caves that were either used for tombs or a place to get out of the blazing heat. Everything seemed to be going great but unfortunately, all good things must come to an end. 

Demise Of Petra and How It Was Rediscovered

On May 19th 363 AD, a massive earthquake occurred that according to a letter wrote by a Jerusalem bishop, destroyed half of Petra. Ultimately, one would think this could be the cause of the demise of the Nabataeans but there has been evidence found that this civilisation survived at least 300 years or so after the fault rupture (Smithsonian, 2007). The evidence is in the construction of new buildings just across the main street to the Great Temple. In one of the post-earthquake churches, they found evidence that a vibrant civilisation lasted until at least seventh century A.D, after which pretty much the whole city was abandoned. This is a completely different outcome to what I had put my bets on given the marine flood sediments found throughout the city. 

The city was then completely abandoned for at least 100 years until it reemerged in the 19th century as a tourist destination for western travellers (Smithsonian, 2007).  

References

Geotimes, 2004, Petra: An Eroding Ancient City, viewed: 16/10/2016, http://www.geotimes.org/june04/feature_petra.html

Nabataea, Petra Water Works, viewed: 16/10/2016, http://nabataea.net/waterw.html

National Geographic, 2015, "Lost City" of Petra Still Has Secrets to Reveal, viewed 16/10/2016, http://science.nationalgeographic.com/science/archaeology/lost-city-petra/

Smithsonian, 2007, Reconstructing Petra, viewed: 16/10/2016, http://www.smithsonianmag.com/history/reconstructing-petra-155444564/?no-ist=&page=2

Wikimedia Commons, 2005, Petra Aqueduct, viewed:  16/10/2016, https://commons.wikimedia.org/wiki/File:Petra.aqueduct.jpg

Bibliography and Recommended Reading

http://www.smithsonianmag.com/history/reconstructing-petra-155444564/?no-ist=&page=2

-This website has a lot of awesome information on how the Nabataeans lived and funnily enough, about the real estate back in the day. 

http://rsta.royalsocietypublishing.org/content/368/1931/5249