Its steep slopes are formed by the over 100 m thick lower Muschelkalk, popularly also called Wellenkalk, from which several solid limestone banks emerge (see also Geology of the Middle Saale Valley).

Without archaeological investigations it cannot be decided whether the relatively flat and rather irregular ground undulations and incisions to the east of the two hillforts mentioned are natural, geological phenomena or actually artificially created or at least expanded fortifications.

The first excavations and recoveries of read finds were carried out by the founder of prehistoric and early historical research in Jena, Friedrich Klopfleisch, in the 1870s and 80s.

In 1983 and 2002, further finds were deposited in the Museum Weimar, which could be picked up during the cultivation of the inner surface for the subsequent afforestation or recovered during a renovation of the inner blind wall.

In spring and summer 2003, Tim Schüler of the Thuringian State Office for the Preservation of Monuments and Archaeology undertook geophysical measurements.

An area of several square meters at the southern end of the plateau between the two hillforts was investigated using geomagnetics, and the absence of areal features was confirmed.

In 1972, Klaus Simon presented a large part of the find material and a description of the prehistoric fortification in the course of his reappraisal of Hallstatt period sites in eastern Thuringia.

The fortification, the remainder of which was preserved in the western hillfort, consisted of a wooden-reinforced fill of stream limestone, which was quarried on the uppermost valley level of the Pennickental, about 80 m below the plateau.

The back front was probably not designed as a ramp, as Neumann assumed, but apparently consisted of a wooden (plank) wall that later tilted inward.

Like the Dohlenstein near Kahla, the Felsenberg near Pössneck or the Weinberg near Oberpreillipp, the Johannisberg near Jena-Lobeda gradually lost its function in the late Hallstatt period and was abandoned as a settlement site.

In 1909 Alfred Götze evaluated the fragments of Slavic pottery already recovered by Klopfleisch merely as isolated finds and considered the fortification remains on the Johannisberg not as early medieval, but generally as prehistoric, in the special case as Bronze Age: "A part of our castle hillforts is Bronze Age, especially those which are called fire or slag hillforts, because they show a strong influence of fire".

It was followed by experts such as Klopfleisch's successor Gustav Eichhorn, Kurt Schumacher, Walter Schultz and almost literally Alfred Auerbach as well as by local historians from the middle Saale Valley.

The dating of the site to the Bronze Age is certainly also the main reason why the castle on the Johannisberg did not play a role in the mostly bitter debates at the end of the 19th and in the first half of the 20th century about the relations between Franks/Germans and Slavs on the Saale.

It will not least be due to the circumstances of the time that Neumann's address of Johannisberg as a Slavic castle wall could not at first gain acceptance, not even among archaeologists and historians with whom he was in close contact such as Werner Radig or Herbert Koch.

Since then, research has almost always focused on the question of whether the early medieval castle on Johannisberg was a fortification of politically independent Slavic rulers or whether it had been built under France.

The excavator Neumann regarded Johannisberg as a Sorbian fortification for the protection of the Saale border solely on the basis of historical considerations and thought that it might have existed between 751 and 937.

[22] In 2006, Tim Schüler opined, "The finds speak for a Slavic fortification that served to secure the middle Saale Valley here in the 9th/10th century.

"[28] However, all these interpretations are based on general considerations about the political situation in the early and beginning high Middle Ages in the Elbe-Saale region rather than on the archaeological finds and features, since their significance in this respect is rather low.

The early medieval find material from Johannisberg is primarily Slavic pottery from the Leipzig district, including five complete and 19 vessels preserved or reconstructable in the upper part, and only a few pieces of metal, stone or bone.

There are several knives with handle tangs and straight or slightly curved backs, which appear especially in the surrounding cemeteries of the 8th and 11th century, but also in numerous castles of this and more recent period.

This is equally true for a knifepoint, an iron arrowhead with a flat, pointed oval blade, an undecorated knife sheath fitting, and two curved strips of sheet metal that can be regarded as ribbon-shaped finger rings.

A high Middle Ages ribbon-shaped handle probably indicates, as do a few other late medieval and modern pottery finds, only a sporadic use of the area in recent times.

Furthermore, it is striking that many comparable fortifications in Central Germany are, according to current research, younger than assumed for a long time, e.g. the (later) Burgward center in Dresden-Briesnitz, the Burgwall "Bei den Spitzhäusern" and the Burgberg in Zehren or the castle on the Landeskrone near Görlitz.

The somewhat older complexes in the other Slavic areas, especially in Great Moravia, are also attributed in recent treatments to the influence of the East Frankish-Carolingian empire or mutual contacts between Franks and Slavs.

The elaborate timber-earth construction with front and rear facing walls testifies to a longer-term use rather than a refuge fortified for a short time.

The traces of building immediately behind the main wall and the peripheral fortifications as well as the central location of the Johannisberg are also indications of a permanent settlement.

Johannisberg is one of the large castles of the Carolingian period, which occur in the entire West Slavic settlement area and show numerous similarities in size, ground plan, wall construction and interior design.

Based on the analogies in the Frankish sphere of power, but also on the few written sources for the West Slavic area, it becomes clear that developed dominions were behind the construction of these fortifications.

Therefore, the question must be asked whether the political-military border between the Frankish empire and the Slavs, the so-called limes sorabicus, ran along the middle and lower Saale at all.

A local history trail, redesigned in 1999, provides information about natural features, geology and the flora and fauna of the eastern slope of the middle Saale valley.