ARCHAEOLOGICAL EXPLORATIONS IN SOSTRA (Ivan Hristov – ivchristov70@abv.bg, Maria Kamisheva) Three construction periods were specified in the castellum. According to epigraphic sources, the first one was related to Cohors II Matiaca stationed in the region after AD 145. The Roman soldiers built the fortification wall, which is 1.20 – 1.30 m in width constructed of ashlars with a core structure of mortar and stones. During the reign of Maximinus Thrax and Gordian III, Cohors I Cispadana was stationed in the region. The destruction of the wall dates to the 230s and happened during the Gothic invasions. Coins minted by Nero, Nerva, Trajan, Antoninus Pius, Commodus and Septimius Severus and bronze fibulae dated to AD 175 – 225 were found in a burnt layer under the northern tower. The second period, when the fortification wall and the towers visible now were built, began at the end of the 3rd century AD, after the Gothic invasions. According to the coins, the construction works were carried out during the time of Aurelian, Probus and Diocletian. Presumably, the second period ended with the Gothic invasions during the reign of Valens. The following buildings functioned during the 4th century AD: the horreum, measuring 32 m by 11 m, built at the end of the 3rd – beginning of the 4th century AD and existing until the mid 5th century AD when it was reconstructed into dwellings; the principia; the praetorium, measuring 400 sq m; via sagularis, c. 7 m in width, discovered at the eastern and southern fortification walls. Via pretoriana is 4 m in width and it runs from the eastern gate of the castellum to the entrance of the principia. Via principalis, running between the southern and the northern gates, and via quintana were also explored. The third period began during the reign of Theodosius I and ended with the destruction of the castellum at the end of the 5th century AD. The latest coin found during the excavations was minted by Zeno. During the third period, buildings situated at the inner side of the eastern fortification wall were constructed and three of the gates of the castellum were closed.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) A section, 15 m long, from the Roman road Ulpia Oescus – Philippopolis was discovered. The road was 7 m wide, situated at 20 m to the east of the fortification wall of castellum Sostra. The road had a curb built of ashlars and was paved with boulders. A pit was explored, containing Late Antique sherds and a copper coin of Valens. The earliest eastern fortification wall was documented, constructed by the soldiers of Cohors II Matiaca during the second half of the 2nd century AD. The wall was 1.90 m wide and c. 130 m long, with foundation 0.40 – 1 m deep, built of boulders bonded with mud. Two rectangular towers were probably situated from its inner side. The beginning of the construction of the castellum dated to c. AD 147 with an order by Antoninus Pius, according to the inscription on an altar discovered in Sostra. The ditch of the early castellum was documented, with V-like cross-section, 5 m wide and 2 m deep. It contained sherds of the second half of the 2nd century AD and a provincial bronze coin of Caracalla, dating the filling of the ditch and the construction of the later fortification wall of Sostra during the reign of Septimius Severus or a little bit later. The second construction period of the castellum dated to AD 200 – 250. In that period, the soldiers of Cohors II Matiaca were still stationed in the castellum and in AD 198 they placed a votive inscription in honor of Septimius Severus. The third construction period of Sostra began in AD 254 during the reign of Gallienus and lasted at least one decade after his death. The finds from the excavations included coins, a plate from a chainmail, a fragment from a bronze statue and sherds of the second half of the 2nd – 3rd centuries AD.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) The explorations continued in the eastern part of the castellum, in Sectors II – III. There were no houses built to the west of the fortification wall constructed of uneven stones bonded with mud. Probably the early fortification wall, situated in front of the eastern fortification wall of the second half of the 2nd century AD, was temporary. The fact that the construction of the early fortification wall was abandoned could be explained with changing the plans for dislocation of the _cohors_ _milliaria_ with _cohors_ _quingenaria_ instead. The explorations to the west of the fortification wall of the end of the 3rd century AD show the existence of fortification structures and houses. The interior rectangular fortification tower, the second one to the south of Porta Praetoria, dated to the second half of the 2nd century AD. During the second half of the 3rd century AD, the tower was cut by the construction of the late fortification wall and in the 4th century AD it was cut by rooms adjoining the inner side of the eastern late fortification wall. Two streets were documented to the west of the tower. The first one was via sagularis, synchronous to the construction of the earliest military camp by Сohors II Mattiacorum. A barracks was documented close to the street, dated by sherds of the 2nd century AD, a bronze fibula, two denarii of Trajan and Hadrian, a bronze coin minted by a later member of the Antonine Dynasty discovered in a layer with traces from fire. A street of the end of the 4th century AD was documented at 70 cm above the earlier street. Finds from the excavations included bones from domestic and wild mammals, river shells, Roman provincial bronze coins minted by Marcianopolis and Nicopolis ad Istrum, bronze plates from plated mails, a fragment from small votive relief, a gold finger-ring and pottery of AD 150 – 250.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) Mansio Sostra was shown in Tabula Peutingeriana. It was located on the road from Ulpia Oescus to Philippopolis and was built during the reign of Marcus Aurelius. Tumuli, mausoleum, part from the castellum, an Early Christian basilica, a sanctuary of the Thracian Horseman, parts from the Roman road and buildings in the vicus located close to the castellum were explored from 1979 to 2013 with some interruptions. The Roman mansio was discovered in 2014. In Sondage No. 1, in Sector A part of a room was explored. It was built in mortared rubble and had a hypocaust with terracotta pipes used for _pilae_ and _tubuli_ within the walls. A coin of Septimius Severus was found in a layer with traces from fire. Judging from the pottery, the room dated to AD 150 – 250. In Sector B, a _praefurnium_ of another room situated to the south of the first one was documented. In Sector C, a hypocaust, the western wall of the room and the _ suspensura _ were discovered. A pool, 7 m by 3.50 m in size, and a room located to the south were discovered to the east of Sondage No. 1. They belonged to baths, probably destroyed c. AD 250 during the invasions of the Goths, judging from a coin hoard and other coins minted in AD 200 – 250 in the towns of the Provinces of Moesia and Thracia, discovered in a layer with traces from fire. A colonial bronze coin of Faustina the Younger minted in Philippopolis was discovered within the mortar floor of the room. Bronze coins of Antoninus Pius, a gold bead, sherds from an anthropomorphic terracotta unguentarium, bone hair pins and sherds from red-gloss pottery were found in the drain of the pool. A building consisting of parallel rooms arranged in a line was discovered at 20 m to the south of the mansio. It was over 25 m long with walls 60 cm wide and built in mortared rubble. A portico and rooms were discovered to the north of the building. Judging from the coins and the pottery, the buildings dated to AD 150 – 250. The earliest coins were minted from Antoninus Pius to Commodus and the latest ones were minted by Philip the Arab.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) Archaeological excavations were carried out in front of the eastern fortification gate of Castellum Sostra. The finds included fragments from building ceramics and sherds of the 3rd century AD, coins of the beginning of the 3rd century AD, predominantly bronze coins of the Severan dynasty, a fragment of a votive relief showing a lion, a fragment of a column and a fragment from a gold finger-ring. A pavement of boulders which belonged to the Roman road Ulpia Oescus – Philippopolis was discovered in Sondage No. 6. A layer containing fragments of Late Antique building ceramics and sherds and a copper coin of Arcadius was discovered and another layer of the end of the 3rd century AD was documented beneath. A layer of small crushed stones was discovered above the Roman road and a hoard of 16 colonial bronze coins from Septimius Severus till Gordian III minted in Nicopolis ad Istrum, Marcianopolis and Hadrianopolis was discovered under it.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) The explorations in Mansio Sostra continued. It was situated at 200 m to the northeast of Castellum Sostra. The praetorium dated to the 2nd – 3rd centuries AD and consisted of c. 12 rooms. Room E was 30 sq. m in size. Its walls were 60 cm wide, built of roughly-cut stones bonded with mortar. Suspensura 23 cm thick was discovered and a hypocaust beneath with terracotta _pillae_, 62 – 70 cm high and 20 cm in diameter, was explored. The room had an entrance on the southern wall, 1.39 m wide; it was walled in the middle of the 3rd century AD or later. An opening towards a furnace was discovered on the eastern wall of Room E. The finds included coins of the middle of the 2nd century AD, sherds from local red-gloss pottery of AD 150 – 250, a roof-tile with a stamp that reads: COH, but without numerals identifying the cohort and probably, it referred to Cohors II Mattiacorum. A layer of collapsed roof-tiles and burned wooden beams was discovered between the pool and the praefurnium and Rooms E and D; coins of AD 150 – 200 were found beneath. Room F (praefurnium) 8 m by 4 m in size was explored. The openings for the furnaces towards the hypocaust in the neighboring Room I were documented in the southwestern and the southeastern corners of the praefurnium. Nine rows of _pillae_ of rectangular bricks, circular bricks and circular terracotta pipes from the hypocaust were discovered in Room I. The average distance between the _pillae_ was 33 cm. The suspended floor was c. 35 cm thick. A small pool was discovered in Sector C, situated close to the large pool in the figidarium.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) Explorations were carried out in front of the eastern fortification wall of castellum Sostra. A sector of the Roman road was explored, 7 m wide and with two lanes. The road was paved with slabs 10 – 20 cm thick, which were placed over a layer of boulders c. 20 cm thick. There was a trampled layer of rubble up to 10 cm thick spread beneath the boulders. Bronze colonial coins were found between the boulders, minted by Septimius Severus, Elagabalus, Severus Alexander and Gordian III in Marcianopolis, Nicopolis ad Istrum, Pautalia and Hadrianopolis. The coins were found as single items and hoards from 9 to 45 coins. A layer containing debris from Late Antique buildings (fragmentary building ceramics, pieces of charcoal) and coins of Theodosius I and Arcadius was discovered over the road. A sondage was carried out between the road and the fortification wall of the end of the 2nd century AD. Debris of the fortification wall of the end of the 3rd century AD and debris of the fortification wall of the end of the 2nd century AD were found. A _colonna miliaria_ was discovered. It had a Latin inscription that reads: “To Emperor Caesar Marcus Iulius Philippus pious, fortunate Augustus, great Persian, great Parthian, with Tribunal power, father of the fatherland, Proconsul, and to Marcus Iulius Philippus, the most noble Caesar, his son; with the cares of Prastina Messalinus, Augustan Legate, Propraetor. 1 mile”. The inscription dated to AD 244. The reason for the column to be erected might have been the passing of Philip the Arab through the Balkans during the summer of AD 244. The name of the Legate Prastina Messalinus is also known from a votive inscription devoted to Philip the Younger by Cohors I Cilicum in Sacidava and from provincial bronze coins of Philip the Arab minted in Marcianopolis.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) The explorations were carried out in the northeastern sector of the castellum. A line of military barracks of the 2nd century AD were documented close to via praetoria to the west of the eastern fortification gate. Building No. 3 was situated close to the northern fortification tower of the eastern gate and adjoined the inner side of the fortification wall. The finds included red-gloss sherds, bronze Roman provincial coins and denarii of Septimius Severus and Philip the Arab, a posthumous copper coin of Claudius Gothicus, a fibula. Via sagularis was discovered beneath a layer with traces from fire, dated by an as and a denarius of Trajan and an as of Faustina the Younger. Building No. 9 measured 4.60 m by 6.20 m and was constructed in rubble masonry with an upper part built of sun-dried bricks. It was situated at 3.90 m to the west of the inner side of the fortification wall. The finds included sherds, bronze Roman provincial coins of Caracalla, Macrinus and Gordian III, a copper coin of Maximian, copper coins of the AD 370s – 380s. Building No. 4 measured 9.60 m by 4 m, constructed of roughly-cut stones and situated at 7 m to the north of Building No. 9. Its walls were preserved at almost 3 m in height, including part of the second floor. The finds included Late Antique sherds, denarii and bronze Roman provincial coins of Macrinus and Gordian III, copper coins of Valentinian I and Valens. The two towers that flanked the northern fortification gate were rectangular, situated at 5.30 m from each other, while the gate was 3 m wide. The towers were additionally built at the fortification wall at the end of the 4th century AD, just before the Gothic invasions. The western wall of the western tower was 2 m wide, while its other walls were 1 m wide. Late Antique sherds and coins of the end of the 4th – first half of the 5th centuries AD were found in the eastern tower. A bronze coin of Probus was found in the mortar of the fortification wall. During the previous excavations, a number of copper coins of Claudius Gothicus and Aurelian were discovered in the mortar of the fortification walls and towers. These coins indicated the date of the construction of the fortification.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) Excavations were carried out in Sector III of Castellum Sostra, situated on the Roman road Ulpia Oescus – Philippopolis. Building No. 7 was explored, situated close to the southern fortification gate, adjoining the northern wall of the western tower. The building measured 15 m by 10 m and was two-storey. It had four rooms on the ground floor with walls built in rubble masonry and preserved up to 2 m in height. Its foundations were dug into a stratum of AD 150 – 250. Building No. 7 was constructed after the southern fortification wall was built after the AD 270s. Judging from the coins and the pottery, the building existed until the end of the 4th – first half of the 5th century AD.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) The earliest fortification wall of Sostra was probably built by soldiers of Cohors II Matiaca during the second half of the 2nd century AD. The eastern fortification wall was 1.90 m wide and c. 130 m long. Geophysical surveys were carried out with Lidar for locating any fortification towers and other structures. Sector A covered an area of 550 sq. m, situated between the southeastern circular tower of the castellum of the 3rd century AD and the southern tower flanking the main eastern fortification gate. To the east, the sector reached the earliest fortification wall of the military camp. Sector B covered an area of 375 sq. m, situated between the northern tower flanking the eastern fortification gate of the castellum and the northeastern circular tower. To the east, the sector reached the earliest fortification wall of the military camp. Sector C covered an area 5.60 m wide and 15 m long, situated to the south of the eastern tower flanking the main southern gate of the castellum. The surveys documented the extension of the earliest fortification wall to the northeast of the northern tower flanking the eastern fortification gate of the castellum and to the south of the southern fortification gate of the castellum.

SOSTRA (Ivan Hristov – ivchristov70@abv.bg) The excavations continued in front of the eastern fortification wall of the second half of the 3rd century AD. A pavement towards the main gate of the castellum was documented, dated by coins of the 3rd – 4th centuries AD. Sectors of the so-called early wall were discovered; it was 1.90 m wide, built of stones bonded with mud, situated at 10 m in front of the eastern fortification wall of the castellum. This wall was later than the first fortification wall of the mid 2nd century AD. Probably, it was built during the second half of the 3rd century AD; it was not more than 1 m in height and was situated in front of the eastern and the northern fortification walls of the castellum. Room D in Building No. 7 situated behind the southern gate of the castellum was thoroughly explored. A layer of collapsed fragmentary sun-dried bricks of the second floor of the building was discovered. The finds included a ceramic jug, coins of the first half of the 3rd century AD, and a hoard consisting of iron tools (a reaping hook, picks, a hoe, chisels, a ploughshare and padlocks), two silver bracelets, two bronze bracelets and two silver earrings, dated to the end of the 4th century AD. A stone pavement with a kerb, parallel to the main road, was documented; a bronze plate of a plate mail and coins of the 3rd – 4th centuries AD were found over the pavement.