The most valuable and intriguing find is an ancient Trakian mask dated about V-IV century beofre Christ. It is resotered and is being kept in the National Historical Museum in Sofia.
From 1900 to 2003, on the territory of the Roman castle and roadside station Sostra were found 12 full or fragmented epigraphical monuments, most of them from the II and III century. In chapter III of the volume, are classified and described all of the known epigraphical monuments till 2003. The presented monuments can be divided in three relative groups:
I. Official inscriptions, raised by the commanding officers of the cohorts stationed in Sostra.
III. Votive offering inscriptions, devoted to different gods from the Greek - Roman and Thracian pantheon. The earliest and most valuable epigraphical monument is found in the year 2001 in the principia of the castle. It is a base of an emperor\\\'s statue, with 9 rows Latin inscription on it. From this inscription we learn, that about the year 14-15 AD, during the rule of emperor Antonin Pee, at Sostra has been billeted the first impressive, for these times, militari unit - II Matiacian cohort, consiting of 1000 infantryman. This subdivision is also connected with the building of the castle in the beginning of the III century.