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@@ -164,9 +164,11 @@ More emotionally charged conversations can be had about converting the United St
 % 113M acres / 5.1 ~= 22M acres
 
 \section{Example: How big could Tenochtitlan have been?}
-The questions described thus far have largely been centered within a physics context.  The paper closes with two more examples that leverage this food energy picture to make historical claims.  The first example relates to the pre-columbian capital of the Aztec Empire, Tenochtitlan, now known as Mexico City.  Tenochtitlan was build on and around a endorheic lake, Texcoco.  Crops were grown in shallow parts of the lake via chinampas, floating patches of decaying vegetation and soil.  Given the proximity to water and decaying vegetation, these fields were very fertile and productive.  
+The questions described thus far have largely been centered within a physics context.  The paper closes with two more examples that leverage this food energy picture to make historical claims.  The first example relates to the pre-columbian capital of the Aztec Empire, Tenochtitlan, now known as Mexico City.  Tenochtitlan was build on and around a endorheic lake, Texcoco.  Crops were grown in shallow parts of the lake via chinampas \cite{national_geo}, floating patches of decaying vegetation and soil.  Given the proximity to water and decaying vegetation, these fields were very fertile and productive and some continue to be used in the present day \cite{google_earth}.  
 
-Estimates of Tenochtitlan's population in 1500CE vary widely, from 40,000 \cite{40k} to more than 400,000 \cite{400k} inhabitants, comparable in size to Paris at that time. These estimates come from oral and written records and estimates of archeological building density and land area.  
+Estimates of Tenochtitlan's population in 1500CE vary widely, from 40,000 \cite{40k} to more than 400,000 \cite{400k} inhabitants, comparable in size to Paris at that time. These estimates come both from oral and written records and estimates of archeological building density and land area.   While canibalism was part of Aztec religious ritual and practice \cite{Aztec_Cannibalism}, the staple Calorie sources for the Aztecs were corn and beans.
+
+Few if any Native American cultures made use of draft animals before the Columbian Exchange.  This means that the food that fed Tenochtitlan must have been brought to the city center by foot or canoe.  How much land must have been devoted to chinampas to feedg the population, or conversely, how many people could be supported by the land within walking or paddling distance from the city center?
 
 \section{Example: Was the Irish Potato Famine a Natural Disaster?}
 
@@ -340,6 +342,17 @@ Dr. Kathleen Delate, assistant professor, Depts. of Horticulture \& Agronomy
 Dr. Cynthia Cambardella, soil scientist, USDA National Soil Tilth Lab 
 Bob Burcham, farm superintendent, Neely-Kinyon Research and Demonstration Farm
 
+\bibitem{national_geo}
+\url{https://www.nationalgeographic.com/magazine/article/in-mexico-city-the-pandemic-revived-aztec-era-island-farms}
+National Geographic
+In Mexico City, the pandemic revived Aztec-era island farms
+ALEJANDRA BORUNDA
+CÉSAR RODRÍGUEZ
+JUNE 30, 2022
+
+\bibitem{google_earth}
+Chinampas are still visible in sattelite imagery.  See for example latitide=19.268, longitude -99.087
+
 \bibitem{40k}
 Susan Toby Evans. 
 2013.