Demografía histórica

http://historicalstatistics.org/

https://en.wikipedia.org/wiki/Medieval_demography#Early_Middle_Ages

www.historicalstatistics.org/Currencyconverter.html

https://magnet.xataka.com/why-so-serious/cuanto-vivia-persona-1850-que-significaba-realmente-esperanza-vida-42-anos