Hillfort builders in pre-Roman eras made an extra effort to give oblique form to the hills on which they built forts. This was the most justified shape from the military-strategic point of view. Obliquity also enabled optimal conditions for spotting any attackers, day and night. .Pictured above is a pre-Roman (Celtic, 2500 years ago) hillfort Ipf, Germany. Oldest artifacts found on Ipf are dated to Late Bronze Age (3200 years ago). This layered-cultures situation is normally found at hillfort sites, and Visočica is no exception, with one important difference however: Visočica (pictured below) is not shaped obliquely but (semi-)rectangularly instead! Since the shaping of hills meant difference between life and death, it's only normal to expect that the Romans too had shaped hills for the same military purposes as civilizations before them had, in their own way and according to their own technical knowledge and military doctrine. (I pointed out in my earlier post below that rectangularity was the favorite layout form in the Roman Empire).
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Visočica hill seems man-shaped so that its slopes run parallel to World lines. This orientation creates optimal conditions where the slopes' edges under moonlight could never create shadows large enough to enable the intruders to climb up the hill carrying their siegecraft equipment unnoticed. (Obviously, this was of little importance in sunlight).
In the only manual of Roman military institutions that has survived intact, called "Epitoma rei militaris" (A Summary of Military Matters), its writer Flavius Vegetius Renatus notes with sadness (at the sunset of the Roman Empire, around 390 AD) "It may be said that our troops for many years past have not even fortified their permanent camps with ditches, ramparts or palisades. The answer is plain. If those precautions had been taken, our armies would never have suffered by surprises of the enemy both by day and night (...) All the barbarous nations range their carriages round them in a circle, a method which bears some resemblance to a fortified camp. They thus pass their nights secure from surprise. Are we afraid of not being able to learn from others what they before have learned from us? At present all this is to be found in books only, although formerly constantly practiced.".
We learn from the above that, by the sunset of the Empire, Roman legions had lost sense of importance for fortifying their camps. But more importantly, we also learn that they didn't have appreciation for circular formation as an aid to their defenses - at all. Indeed, as notable scholars of today note, rectangular layout was a preferred geometrical form for construction works in the Roman Empire (see the yesterday's post below). .The matters in the Vegetius's work most relevant for the Visočica case are contained in Books IV and V. Book IV in general deals with fortifications and sieges, so that its Section 24. titled "On saps, whereby the wall is undermined or the city penetrated" is entirely dedicated to sapping via underground tunnels and "mines". Book V describes the astronomy, navigation and tide knowledge of the Roman army and navy. The Vegetius's work has been used frequently for the education at military academies. The Books III-V greatly influenced the medieval world, while an unusually high number of 226 manuscripts of the Latin text survived to this day. Given the intensive military activity on the Balkans peninsula over the last several millennia, it's obvious that able generals and rulers of long-durable medieval Bosnia also must have had substantial knowledge of the Vegetius's work (translated into seven languages by 1450-ies, that is by the fall of Bosnia under Ottoman occupation). But so did their adversaries (Serb; Ottoman), so that the tunnels found inside Visočica likely have been used/amended by the attackers (for sapping) as well as by the defenders (for water supply and counter-mining) of a medieval Bosnian city the remains of which indeed sit at the Visočica summit.
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Finally, speleothems found so far inside the tunnels under Visočica or its surroundings had grown less than a decimetre. Even without exactly knowing the speleothems' growth rate in the area, this finding strongly suggests that the tunnels could hardly be older than the Antiquity.
.(Note that the first modern edition of "Epitoma rei militaris" in English includes just the first three of the total of five books of Vegetius' work. The fourth and fifth books have not been included in the first modern translation by Lieutenant John Clarke, London 1767. As the alleged reason for this illogical move, the publisher stated that "both very brief, the IV and V book deal with the attack and defense of fortified places and with naval operations. These are of interest only to military antiquarians and for that reason have not been included in this edition." This was unjustified because printing costs of not including two reportedly shortest parts of a rendering must be relatively minute. Also, these were in fact the most practical and technically most detailed parts of all five books! Besides, being a translation of the only entirely preserved source on Roman military, it's hard to understand why it too shouldn't be complete. Luckily, the best, 2004 English translation by M.D. Reeve of Cambridge contains all five books.)