Ajdovski zid (“Ajdovski wall”) above Vrhnika is the longest known section of the Late Roman claustra Alpium Iuliarum barrier system. It measures over 6,700 m in length and has at least 35 barrier towers. The ancient Vrhnika (Nauportus) was enclosed underneath it, where a smaller Turnovšče fortlet might have been included in the barrier system as well.
The Ajdovski zid barrier, which is located above the westernmost edge of the Ljubljana Marshes, was the first in a series of barrier walls that controlled the main Roman road Emona – Aquileia. In the southwest it starts at the crossing between the Javorč Hill and the Ljubljanski vrh Hill, above the present-day railway station Verd. Ajdovski zid wall runs southwest along the northern slope of the Ljubljanski vrh Hill, where it ends just below the peak on the steepest slope. We can follow it again after roughly a kilometre on the south-western slope, where it crosses the mountain pass and continues on the slopes of the Bukov vrh Hill, from where it descends into the valley. There it is intersected by the Ljubljana – Logatec highway, which directs the wall over the Suhi hrib Hill on the other side. In the saddle of the Raskovec Mountain it crosses an old macadam road between Ljubljana and Trieste and ends at the top of the Raskovec Mountain. It continues on its north-western slope, over the Cesarski vrh Hill, where it was destroyed by 3 traffic lines at the distance of 200 m – the old and the new roads called Tržaška cesta and the railway. On the other side, the wall rises along the slope of the Smrekovec Mountain, turns to the northwest in the form of an arch and leads to the Strmica Mountain and then descends into the hamlet of Zaplana. Due to the construction of the infrastructure, the barrier there is destroyed to a large degree. The last section of the wall can be followed along the southern slope of the Špik Mountain, where the wall ends beneath the top of the mountain.
The barrier wall is approximately 1 m wide on the entire route and in some places the outlines of the supports are also visible alongside it. The towers, which were about 100 m apart from each other, were positioned on the inner (western) side of the barrier and their sides were 4–5 m long.
The view of the Ajdovski zid barrier was impeccable due to its shape, as all the strategic points on the wall were visible to one another. A good view of the surrounding area was also possible from the entire barrier – the Ljubljana Marshes, the Polhov Gradec Hills (Polhograjsko hribovje) and the Rovte Hills (Rovtarsko hribovje) were visible as well as the Logatec Plateau (Logaška planota), the Menišija Plateau and the edges of the Hrušica Massif (Hrušiški masiv) in the hinterland. The barriers in Rakitna and Pokojišče are also visible from the Ajdovski zid barrier.