De expugnatione Lyxbonensi

De expugnatione Lyxbonensi ("On the Conquest of Lisbon") is an eyewitness account of the Siege of Lisbon at the start of the Second Crusade, and covers the expedition from the departure of the English contingent on 23 May 1147 until the fall of Lisbon on 28 June 1148. It was written in Latin by one Raol, an Anglo-Fleming and probably a chaplain of Hervey of Glanvill in the army from East Anglia. It is an important source for the organisation of the crusade, especially among the middle ranks of society. An English translation by Charles Wendell David appeared in 1936 and was reprinted in 2001.

De expugnatione is untitled in its sole manuscript. Its first English editor, William Stubbs, gave it its modern title, which was picked up by Charles Wendell David, who preferred it for its similarity to the titles used by the Lisbon Academy, by Reinhold Pauli for his German edition of some excerpts, and in the bibliographies of August Potthast and Auguste Molinier.Charles Purton Cooper, in recognition of the text's form as an epistle, designates the it Cruce Signati anglici Epistola de expugnatione Ulisiponis ("English Crusaders' Letter on the Conquest of Lisbon").

The unique manuscript was believed by Stubbs and Pauli to be the original autograph. David suggests however that it was not the original, which was probably written hastily during the crusade, but rather a later autograph edited by the author later, perhaps in his old age.

The author of the De expugnatione names himself in his opening lines, although in an obscure abbreviated form that has perplexed scholars: Osb. de Baldr. R. salutem. Since at least the time of Matthew Parker he has been known as "Osbern" and the manuscript's table of contents, written in a Renaissance hand, lists the work as Historia Osberni de Expeditione etc. ("Osbern's History of the Expedition, etc."). This purely conjectural name has been oft repeated and has become traditional.

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