San Giovanni in Laterano

"Giessen Anonymous"  a German cleric from Mainz?
Letter to an unknown person

"Serenitati vestre"

Giessen, Universitätsbibliothek 1105, fol. 59ra-60va

Stephan Kuttner and Antonio García y García,  "A New Eyewitness Account of the Fourth Lateran Council,"  Traditio 20 (1964) 115-178 at  128
ostea tractatum de negocio sancte crucis et expedicione signatorum, firmissma pace ipsius constituta et inducta .  .  . Deinde leguntur constitutiones domini pape.  Quibus perlectis cum iam plus quam nona hora diei esset, magnam partem de ligno sancte crucis de Constantinopoli allato omnibus demonstravit. 
After having dealt with the crusade and the crusaders' expedition, with a solid peace having been established .  .  . finally the constitutions of the Lord Pope were read.  The constitutions having been recited, since it was after the ninth hour of the day a large piece of the wood of the holy cross from Constantinople was displayed to all.