The Rythmus de captivitate Ludovici imperatoris ("Poem on the Captivity of Emperor Louis") is a short alphabetic acrostic poem in Middle Latin lamenting the capture of Louis II, King of Italy and Emperor of the Romans, on 15 August 871.
He returned in triumph to Benevento, but his presence there and that of the Empress Engelberga, alienated the local nobility.
Adelchis, the prince of Benevento, put the imperial couple under arrest.
As a condition of their liberty, Louis swore an oath never to return to Benevento.
[2] The Rythmus de captivitate Ludovici imperatoris places the blame for Louis's humiliation on his own captive, Sawdan, who is said to have prodded Adelchis into action.