The Cathedral Treasury (Domschatz) and the DiocesanMuseum of Limburg (Diözesanmuseum) share a common building not far from theCathedral Square. Founded in 1905, the museum was originally dedicated to thehistory of the Catholic bishopric creation in Limburg in 1827. But in 2011 the permanentexhibition was expanded and now the works of sacred art are displayed there.
The mostvaluable exhibits of the Diocesan Museum contain the X century Byzantine staurothekewith the Holy Cross in it. A reliquary, decorated with precious stones andenamel, consists of an ark with grooves to hold the Cross and a special lid tocover the priceless relics. It was brought to Germany in 1208 by the participantof the Fourth Crusade knight Heinrich of Ulm who handed the relic over to theStuben Monastery. When the monastery was dissolved at late XVIII century, therelic found itself in the Ehrenbreitstein fortress, and later it became theproperty of the Prince of Nassau-Weilburg, who granted it to the Limburgdiocese in 1835. Since 1959, the Limburg Catholics have been celebrating the CrossWeek every year in September, the key topic of which is veneration of therelics kept in the city.