The Lower Danube Roman Limes (1st-6th C. AD) - Vagalinski, Liudmil Ferdinandov; Šarankov, Nikolaj Stefanov; Torbatov, Sergey (National Archaeological Institute with Museum, BAS, 2012)
"The present volume is dedicated to the XXII International Limes Congress which will be held for the first time in Bulgaria, in the Danube city of Ruse (Roman 'Sexaginta Prista') in September this year ... in the city of Sofia." - preface.