View source for 840s

==References==
===Citation===
{{Reflist}}
===Bibliography===
*{{Byzance et les Arabes | volume = 1}}
*{{The Byzantine Revival, 780–842}}
* {{EI2 | title = Lamas-Ṣū | first = Cl. | last = Huart | authorlink = | volume = 5 | page = 647 | url = http://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-2/lamas-su-SIM_4631}}
* {{citation | last = Jones | first = Gwyn|title= A History of the Vikings|year=2001|publisher=Oxford University| isbn = 978-0-19-280134-0 | url = https://books.google.com/books?id=lD74bDG3O5oC | mode=cs1 }}
* {{cite book | last = Kennedy | first = Hugh | author-link = Hugh N. Kennedy | title = When Baghdad Ruled the Muslim World: The Rise and Fall of Islam's Greatest Dynasty | location = Cambridge, MA | publisher = Da Capo Press | year = 2006 | isbn = 978-0-306814808 | url = {{Google Books|67fZB5YGkOQC|plainurl=y}} }}
* {{citation | last = Sawyer | first = PH |title=Illustrated History of the Vikings|year=2001|publisher=Oxford University|isbn = 978-0-19-285434-6 |url=https://books.google.com/books?id=nJqf8e1vHFgC | mode=cs1 }}
* {{cite book | last = Toynbee | first = Arnold | author-link = Arnold J. Toynbee | title = Constantine Porphyrogenitus and His World | year = 1973 | location = London and New York | publisher = Oxford University Press | isbn = 0-19-215253-X}}
* {{Cite book|last=Goldberg|first=Eric J.|title=Struggle for Empire: Kingship and Conflict under Louis the German, 817-876|year=2006|location=Ithaca, NY|publisher=Cornell University Press|isbn=9780801438905|url=https://books.google.com/books?id=oyiTg0wgl58C}}
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