When the names of the churches were forgotten, the villagers gave them new ones. The Letters. God's Gully. The Buried Church. One they called simply The Church, a name so stripped of detail it somehow contains everything that had been lost. Centuries of monastic life, a scriptorium full of manuscripts, royal burials, eight hundred monks – all of it reduced, in the end, to a name that was really just a gesture toward something irreplaceable and gone.

Churches and monasteries hewn into rock at often precipitous heights were one of the more ingenious solutions that Christians across the Balkans and the Middle East devised over centuries: abodes removed from the crowd, built in places where conventional construction was barely possible. Since the early centuries of the religion they enlarged existing caves into rooms that resembled church interiors – naves, altars and apses all present. Around these carved sanctuaries they lived in cells, the cells multiplying into large compounds. Tucked into isolated spots, frequently in narrow river canyons, they gave monks what they came for: solitude from laymen and a degree of security from invaders.

Some historians surmise that the Ivanovo murals might have outshone the Italian Renaissance if it were not for the Ottoman invasion

The rock churches of Cappadocia, in Turkey, are the most celebrated example of this tradition, but there is no need to travel to Anatolia to see such structures and their art. Bulgaria has several sites of the same kind. One of them holds a place on the UNESCO World Heritage List.

About 20 kilometres from Ruse, the bends of the Rusenski Lom River embrace a dozen or so churches and monastic cells carved into the limestone cliffs. Between the 12th and the 14th centuries they formed a single monastic compound of considerable size and influence. Today, largely empty of the life that once animated them, they are among the most quietly affecting places in Bulgaria.

There is a bonus to visiting that has nothing to do with history. The Ivanovo Rock Churches sit within the Rusenski Lom Nature Park – a place of steep wooded gorges, unusual rock formations and the persistent sound of running water, home to a number of rare and endangered species. The park covers over five acres of some of the most dramatically beautiful terrain in northern Bulgaria, and arriving at Ivanovo means passing through it. The beauty of the landscape is not incidental to the story. It explains, at least partially, why monks seeking solitude chose this particular stretch of river in the 12th century.

The complex grew steadily. By the following century it had become a major spiritual centre, attracting royal patronage from the Second Bulgarian Kingdom whose capital, Tarnovo, was relatively close, upstream nearby Yantra River, in the northern reaches of the Stara Planina mountain. During the reign of King Ivan Asen II (1217-1240), a monk named Ioakim secured a substantial royal donation for the creation of the monastery's first rock church. Ioakim and the king were close – when Ivan Asen restored the Bulgarian Patriarchate after two centuries under Byzantine domination, it was Ioakim he appointed as its first head.

That relationship between crown and monastery proved durable. At the height of its existence, the compound counted 40 churches and 300 cells accommodating up to 800 monks. The kings of Tarnovo kept on donating. At least two subsequent rulers – Georgi Terter and Ivan Aleksandar – provided funding and were depicted in murals alongside their wives. Georgi Terter is thought to have been buried here in the early 14th century, his tomb now lost along with much else.

The extraordinary vitality of the Ivanovo monastery was inseparable from the spiritual current of its age: Hesychasm. Born in Byzantium, the tradition spread with remarkable speed across the Balkans. It was a mystical practice, promoting silence and meditation in solitude as the most direct path to salvation – a theology that suited the landscape around Ivanovo well. In the 14th century, Hesychasm gathered so many adherents that Serbian kings were driven to forbid nobles from taking monastic vows, their departure having opened dangerous gaps in the military and the state administration. Historians have argued that the unwillingness of Hesychast culture to engage with the dangers of the physical world contributed, at least in part, to the swiftness of the Ottoman advance in the same century.

Life at Ivanovo was not confined to prayer and mysticism, however. The monastery housed a busy scriptorium, producing bibles and other ecclesiastical manuscripts for churches across the region. The monks copied and illuminated texts – it was a place of intellectual as well as spiritual labour.

The Ottoman invasion ended both. The region became the scene of repeated battles. The monastery was subsequently stripped of its privileges as a landowner, a blow that left the already diminished community without the means to sustain itself. During the 15th and 16th centuries, Ivanovo was abandoned. The elements moved in, as did treasure hunters. The wooden staircases that had once connected the cells and churches rotted away. Rain and frost worked at the paintings on the walls. The names of the churches were simply forgotten.

The murals that survived this long attrition are the reason UNESCO placed Ivanovo on its World Heritage List in 1979, alongside the site's combination of historical importance, natural setting and architecture. The paintings are a fine example of Bulgarian medieval art. They follow the conventions established in Constantinople – the canons of pose, colour and hierarchical arrangement familiar from Byzantine tradition. Yet, they carry something else besides. Although most of depicted figures, if not all, have lost their faces, they poses strike the modern visitor with their inherent humanity. They still keep on with the hieratic Byzantine cannon but they are more humane, more present. Some scholars have been eager to read in this tendency a precursor to the Renaissance, the Tarnovo school anticipating by decades what would emerge in Italy. It is a claim worth treating with some caution, but the impulse behind it is understandable. There is something in these figures that reaches across the centuries with unusual directness.

Bulgarians traditionally explain the deleted faces from old medieval frescoes with the destructive work of Muslims back in the day. However, there is another explanation. In the centuries of the Ottoman domination, local Christians would believe that scraping the eyes of a painted saint and diluting the paint in some water would cure eye illness. The practice has been recorded in both Bulgarian and Greek communities.

What survives of Ivanovo's richness, of course, is a fragment. The ochres and blues that once covered every surface have been reduced, in places, to ghost marks and bare stone. In others, the painted plaster has held with astonishing tenacity. The experience of moving between these states – vivid presence, sudden erasure – gives Ivanovo a quality unlike almost anywhere else in Bulgaria. The silence is the silence of a place that was once genuinely full of monks and manuscripts and the sound of chanting carried out over the gorge, and is now not. 

Located farther downstream on the Rusenski Lom, Basarbovski Monastery is now one of the two rock monasteries in Bulgaria still inhabited by monks. Presumably it originated in the 13th-14th centuries, but the earliest evidence of its existence dates back to 1431, a few decades after the Ottoman invasion