Known as the Danube Bend, the mountains on the right bank of our European-famous landscape have been known for centuries as the Pilis. However, they have very different geological histories, which is why they should be split into two: the Pilis in the south and the Visegrád Mountains to the north.
The Pilis is the eastern most member of the Transdanubian mountain range. The name is of Slavic origin and means bald top, referring to the monks' disembowelled heads (Latin: tonzura). The term perfectly describes the mountain range: the peaks higher than 500 metres, which rise from the forested slopes, have no forest because they lack the soil to support it. The only vegetation here is rocky grassland with low, scrubby, grove-like bushes: the tops are 'bare'.
The rocks that form the mountain range were formed in the first third of the Mesozoic era, at the end of the Triassic. Limestone and dolomite were formed from sediment deposited in a shallow marine environment along the shores of the ancient ocean, two hundred million years ago. This environment persisted for a very long time, up to 40 million years according to professional estimates. However, in later geological ages, the destructive work of external forces has eroded much of the rock layer, which was originally several kilometres thick. According to exploratory drilling, carbonate layers of Triassic age can still be found down to a depth of about one and a half kilometres.
Earth movements up to the present day have uplifted parts of the originally horizontally deposited rock, thus raising the mountain range. Recent tectonic movements have caused these uplifted blocks to fragment and tilt. Today, the mountains of Pilis are steep in the south-west, rocky in the upper part and gently sloping in the south-east, with deep, steep-walled valleys between the clasts. The destructive processes have been very effective: the highest peaks of the mountain range today are just over 700 metres (Great Soplák 710 m, Great Bodzás 717 m, Pilis-tető 756 m), although they may originally have been Himalayan in height.
The interior of the Pilis and the foothills have been inhabited by humans since the Stone Age, so the natural habitat has been profoundly altered by continuous human impact. Deforestation probably started in the Neolithic period and continued during the centuries of the Roman Empire and the subsequent migration of the population, which swept the area away, with the establishment of fields, vineyards and orchards in place of the cleared forests. From the Middle Ages onwards, the remaining forests were used as royal hunting grounds, the hermits in seclusion lived in the wilderness, and only a few intermountain basins developed into small villages, mainly dependent on logging for their livelihoods. One of the most important monasteries of the Palatines was built at Kesztölc, the ruins of which have recently been excavated, and the other famous monastery at Pilisszentkereszte belonged to the Cistercians.
Despite its long history, the proportion of forests in the Pilis is high. The typical mid-mountain submontane beech and hornbeam-oak forests are home to interesting plant species, such as the red-horned huns, which is native to the Eastern Carpathians and reaches the western limit of its range here. The lower mountain slopes, up to two to three hundred metres above sea level, are covered with tannery-oak forests, which also contain a rich fauna of protected species of flora and fauna. The oak and beech forests harbour some very rare orchids and small species of orchids, such as the Rutaceae orchid and the Peitzii orchid, which are found in only a few places. On the upper, sunny parts of the rocky steep slopes, a mosaic of warm-loving oak forests and mossy oak scrub interspersed with rocky grasslands form species-rich habitats. In the limestone rock pools of the Pilis Peak, the Hungarian husk-grass is a relict endemism found only in a few sites of the Carpathian Basin, and in the northern dolomite rocks, the mountain pine-grass is a species found only here in Hungary.
Among the more spectacular protected species of fauna, we should mention the typical beautiful beetle of the oaks, the hornbill, and in the beech forests the national park's heraldic animal, the coniferous zincet, but also the rare and rarely seen inhabitant of the hollow stump-holes, the highly protected blue pine beetle. The sunny, southeast-facing rocky grasslands are home to rare equatorial species: the highly protected Hungarian tarsier and its large relative, the saw-winged grasshopper, are not uncommon in these habitats. The grey ant butterfly, a beautiful protected daytime moth, is a representative of specialised insects in the St. Lazarus tarns, rich in forest steppe meadows, mountain pastures and mountain reed beds.
A typical, rare nesting species of the limestone rocks of the Pilis is the highly protected Peregrine Falcon, which has a stable population in the mountains. Rarely seen is the breeding wasp hawk, which prefers warm oak hillsides. It is a specialist feeder, feeding mainly on membranous winged birds, but also preys on small mammals. The most important fauna of the many caves in the mountain range are the bats that breed and overwinter here. Most of the native species occur here, including the highly protected big-eared bat and the western dirt bat.