This book makes available for the first time the Syriac text of the Judas Kyriakos legend in the manuscript Petersburg/leningrad N.S. 4 and an English translation of this text. The manuscript, which dates from c. 500 C.E., contains the oldest extant Syriac text of the legend of the discovery of the True Cross by Judas Kyriakos and is therefore of great value for the history of the legend of the inventio crucis. The book also makes available again the Syriac text of the manuscript Londin. Bl Add. 14.644 which was first published by E. Nestle in the last century but is now hard to obtain. Also of this text an English translation is offered. The Syriac text and translations which are accompanied by a commentary, are preceded by a long historical introduction on the various 4th/5th-century versions of the legend of the discovery of the Cross (Helena- and Protonike legend), the history of modern research on the inventio crucis legend, on the Syriac manuscript tradition of the legend, on the date and place of origin, as well as on the original language of the Judas Kyriakos legend.