Part of Constantinople on the web section of Elpenor's history resources [15 Pages]
The way in which Dalmatius de Sergy obtained the head of St. Clement is an illustration of the crusader’s belief that the acquisition of a relic and its transport to the West would be allowed as a compensation for the fulfilment of the crusader’s vow. That knight was grievously afflicted that he could not go to the Holy Land, and earnestly prayed God to show him how he could execute some other task equivalent to that which he had sworn, but failed, to accomplish. His first thought was to take relics to his own country. He consulted the two cardinals who were then in Constantinople, who approved his idea, but charged him not to buy these relics, because their purchase and sale were forbidden. He accordingly determined to steal them, if such a word may be applied to an act which was clearly regarded as praiseworthy. The knight, in order to discover something of especial value, remained in Constantinople until Palm Sunday in the following year. A French priest pointed out to him a church in which the head of St. Clement was preserved. He went there in the company of a Cistercian monk and asked to see the relics. While one kept the persons in charge speaking with him, the other stole a portion of the relic.
On leaving, the knight was disgusted to find that the whole head had not been taken, and, on the pretext that he had left his gauntlet behind, a companion regained admittance to the church, while the knight again kept the monk in charge in conversation at the door. Dalmatius went to the chest behind the altar where the relic had been kept, stole the remainder, went out, mounted his horse and rode away. The head was placed with pious joy in the chapel of his house. He returned, disguised, some days after to the church, in order, as he pretended, to do reverence to the relic—in order really to ascertain that he had taken the right head, for there had been two in the chest. He was informed that the head of St. Clement had been stolen. Then, being satisfied as to its authenticity, he took a vow that he would give the relic to the Church of Cluny in case he should arrive safely. He embarked. The devil, from jealousy, sent a hurricane, but the tears and prayers before the relic defeated him, and the knight arrived safely home. The monks of Cluny received the precious treasure with every demonstration of reverent joy, and in the fullest confidence that they had secured the perpetual intercession of St. Clement on behalf of themselves and those who did honor to his head. The relics most sought after were those which related to the events mentioned in the New Testament, especially to the infancy, life, and passion of Christ, and to the saints popular in the West.
Reference address : https://www.ellopos.net/elpenor/greek-texts/fathers/pears-constantinople-1204.asp?pg=13