Nearly halfway between Logatec and Ajdovščina, the Hrušica barrier is located on a local road leading from Kalce to Col. The last barrier line is located at the highest point of the formerly main Roman road Ljubljana (Emona) – Ajdovščina (Castra). The barrier consists of the Ad Pirum fort and the barrier walls that extend hundreds of metres north and south of it. The best viewpoints on the barrier are at the Bršljanovec Hill (at the end of the south-eastern section of the wall), the Listnik Hill (the highest point inside the fort) and the Nivčen grič Hill (the highest point on the northern wall).
Due to its position, the Ad Pirum fort was one of the most important points in the claustra Alpium Iuliarum barrier system and in addition to the ancient Rijeka, it is the richest archaeological site within this system. The fort, through which the main Roman road used to lead, stands on a hilly and wooded terrain with rare water springs. The first signs of settlement date back to the 2nd century at the latest, when the Roman road was already in use and there were mentions of a station called Ad Pirum summas Alpes in this spot, which is 9 miles (15 km) away from Castra (today’s Ajdovščina). During the first critical times in the second half of the 2nd century, a roadside control with adjutants was probably established there, a sort of a police checkpoint. At the latest in the 4th century, the wall of the fort was built, while the barrier on Hrušica was abandoned in the first three decades of the 5th century.
The barrier consists of five sections – a fort in the central part, the northern, south-western and south-eastern barrier walls and the section on Polšakovo kopišče. The total length of the barrier walls is almost 2 km and the fort’s circumference is over 600 m. The main Roman road led directly through the fort and the barrier walls closed the valleys north and south of the pass. The builders effectively used the natural features of the steep slopes and adjusted the course of the wall to the terrain.
The Ad Pirum fort is oval in shape and measures 250 m in length and between 30 and 80 m in width. It consists of the northern and southern parts, which are separated by a transversal wall. Only the lower part was inhabited, through which a road also ran. The towers in the fort were positioned on all corners, except on the south-eastern corner, where the south-eastern and south-western barrier walls were simultaneously attached. An additional tower was also positioned in the centre of the transversal wall and the two entrances to the fort were fortified with two double towers. Two smaller passages, wide enough for only one person, were located by the towers in the north and south.
The northern barrier wall leads from the northern top of the fort from the slopes of the Listnik Hill through today’s macadam road towards the Črni vrh Hill to the Nivčen grič Hill and to the slopes of the Javorjev grič Mountain where it ends. At the peak and on the slopes of the Nivčen grič Hill, two very poorly preserved towers are also located. The south-eastern and south-western barrier walls also descend from the south-eastern corner of the fort. The south-western wall ends roughly 50 metres from the fort in front of a present-day road. The south-eastern wall, which was destroyed by the route of the gas pipeline after some ten metres, descends steeply in the direction of the Bršljanovec Hill. It continues its steep descent to the passable tower with gates, through which a forest path leads on the route of the former Roman side road. Then, the wall, passing by another tower, descends to its lowest point, where it is intersected by a macadam forest trail and from there it steeply ascends again to the slopes of the Bršljanovec Hill, where additional two towers are visible. The wall on the top of the hill soon disappears, but before that, we can observe two more towers on it.
The remains of the wall of the fort and parts of the wall have been conserved and the interior has been almost completely researched. Today, at the Hrušica barrier, there is an archaeological park, a museum exhibition and an archaeological trail, which is about 4 km long, and there is also a catering offer.