Petra

Petra announces itself through a slot canyon. The approach from the visitor centre passes through a series of widening valleys before entering the Siq — a 1.2 kilometre crack in the sandstone plateau, its walls rising in places to 80 metres, its floor following the line of a wadi whose flash floods created the passage over geological time. Light at the end of the Siq is the first glimpse of the Treasury, Al-Khazneh, its carved facade rising 40 metres from the canyon floor in a display of Hellenistic architectural vocabulary carved from the living rock by Nabataean craftsmen two thousand years ago.

The visual effect of that first encounter with the Treasury is one of the most celebrated experiences in archaeology and tourism alike. What requires more time to understand is that Petra is not primarily the Treasury. The Treasury is the introduction to a city of extraordinary scale and complexity — 800 individual monuments carved from sandstone across a dramatic highland landscape of cliffs, wadis, and natural amphitheatres — that unfolds across 264 square kilometres and rewards days of exploration.

The people who built this city — the Nabataeans — were traders and hydraulic engineers of genius. Their achievement at Petra was not merely architectural. It was the creation of a liveable city in one of the most water-scarce environments in the Near East, using a system of channels, pipes, cisterns, and dams that collected and directed every available drop of rainfall across the surrounding watershed. Without that hydraulic system, there would have been no city. And the water that Petra's Nabataean builders managed with such skill is now, in the form of rising groundwater from leaking modern supply pipes, one of the most serious threats to the monuments those builders left behind.

Pre-Nabataean Settlement — The Natural Geography

The landscape that the Nabataeans chose for their capital was already, before any human modification, one of the most dramatic in the Near East. The southern Jordanian highlands are a landscape of deeply incised sandstone — the Nubian Sandstone formation, its cliffs coloured in bands of red, pink, orange, and cream — cut by wadis that drain the seasonal rainfall toward the Wadi Arabah and the Gulf of Aqaba. The natural basin at Petra, surrounded by cliffs that provided both defence and the raw material for construction, sat at the junction of several wadis whose drainage patterns made water collection feasible and whose convergence created a natural crossroads for caravan traffic moving between the Arabian Peninsula, the Mediterranean, and Egypt.

4th Century BCE to 1st Century BCE — The Nabataean Foundation

The Nabataeans, an Arabic-speaking people of likely northern Arabian origin, establish themselves at Petra as a trading community whose livelihood depends on controlling the caravan routes carrying frankincense, myrrh, spices, gold, and luxury goods from the producing regions of Arabia and the Horn of Africa to the consuming markets of the Mediterranean world. Their genius is not merely commercial. It is engineering: the system of channels, pipes, and cisterns they construct to manage the episodic rainfall of the Jordanian highlands — storing water from the rare but intense rainfall events of the winter season in cisterns that maintain the city's supply through the dry months — is one of the most sophisticated water management systems of the ancient world. Without it, the population of 20,000 that the city may have sustained would have been impossible in a landscape where annual rainfall averages 150 millimetres.

The earliest carved structures at Petra reflect an austere Nabataean architectural style — cubic tomb facades with simple stepped crow-step merlons, derived from ancient Mesopotamian and Arabian traditions. As the city grows wealthier and as contact with the Hellenistic world intensifies through trade, the architectural vocabulary becomes more elaborate, incorporating Greek architectural orders — Corinthian capitals, entablatures, pediments — into a distinctively Nabataean hybrid style that reflects the cultural position of a trading people engaged with multiple civilisations simultaneously.

1st Century BCE to 1st Century CE — The Golden Age

At the peak of Nabataean prosperity, Petra controls the most lucrative trade routes in the ancient Near East. The famous products of this wealth — the Treasury, the Monastery, the Street of Facades, the Roman-period colonnaded street — are the material expression of an economic success that made the Nabataean Kingdom one of the wealthiest per capita states of the ancient world. The Nabataean pottery produced during this period, gossamer thin and painted with a distinctive geometric and botanical vocabulary, is one of the finest ceramic traditions of antiquity. Their script, a cursive form of Aramaic, is the direct ancestor of the Arabic script still used across the Islamic world.

The Treasury — Al-Khazneh — is the most celebrated monument of this period, its two-storey Hellenistic facade carved from a single sandstone cliff face with a precision and scale that still impresses. Its function remains debated — a royal tomb is the consensus scholarly view, though later Bedouin tradition believed it contained a treasure hidden by a Pharaoh, hence the name. The bullet marks on the urn at the summit of the facade are evidence of generations of attempts to shoot the treasure loose.

106 CE — Roman Annexation

Rome annexes the Nabataean Kingdom in 106 CE, incorporating it as the province of Arabia Petraea. The transition is peaceful and in many respects beneficial to Petra — Roman investment in roads and infrastructure extends and improves the caravan network, and the city continues to develop. The colonnaded street, the Temenos gateway, and the Temple of the Winged Lions date to the Roman period and reflect both the continuation of Nabataean traditions and the introduction of standard Roman urban planning elements. But the sea trade routes around Arabia, increasingly viable as navigation techniques improved, gradually displaced the overland caravans that were Petra's economic foundation, and the city's population and wealth began the long decline from which it never recovered.

363 CE — The Earthquake

A severe earthquake strikes the region in 363 CE, causing widespread structural damage across Petra and the surrounding area. The ancient sources describe the damage as catastrophic. The city's population was already declining, and the combination of earthquake damage and the continuing diversion of trade to sea routes made full recovery impossible. By the Byzantine period, Petra was a much-reduced city; by the Islamic period, it was essentially abandoned by all but a small pastoral community who made use of the carved chambers as dwelling spaces.

1812 — Rediscovery

Johann Ludwig Burckhardt, a Swiss explorer working for the Association for Promoting the Discovery of the Interior Parts of Africa, was attempting to reach the site of the ancient city he had encountered in the classical sources. Disguised as a Muslim pilgrim and guided by a local Bedouin, he entered the Siq in August 1812 and became the first Westerner to visit Petra in centuries. He could not document the site extensively without revealing that his interest was archaeological rather than religious, but his published account of the visit introduced Petra to European awareness and opened the way for the succession of travellers, artists, and archaeologists who followed.

1985 to Present — World Heritage and Tourism Development

Petra's inscription on the World Heritage List in 1985 coincided with the beginning of a rapid growth in international tourism to Jordan that has made the site one of the most visited archaeological destinations in the world. The infrastructure that accompanied that growth — the hotel development in Wadi Musa, the water supply systems that serve both tourists and the town, the roads and visitor facilities — has also introduced the leaking pipes that are raising groundwater beneath the monuments and the traffic that is vibrating carved surfaces. The Bdoul Bedouin community, who lived in the site's caves and had served as its informal guardians for generations, were relocated to a purpose-built village — Umm Sayhoun — in the 1980s, a displacement that created social complexity and economic dependence on tourism employment that has shaped the management challenges ever since.

The flash floods of October 2018, which channelled through the Siq and surrounding wadis and killed 23 tourists who had descended despite flash flood warnings, were the most visible demonstration of the life safety dimension of a risk that conservation researchers had been documenting for years. The subsequent review of flood management at the site has produced improvements, but the fundamental vulnerability of a tourist infrastructure built in flash flood channels remains.

Petra carries an At Risk classification — a site under significant and measurable pressure, where the threats are active and where the trajectory is concerning but where the situation has not yet produced irreversible damage at the scale of the highest-risk sites.

Flash Flood Risk is the most acute safety hazard and a significant conservation threat. The watershed above Petra is large and steep, and rainfall events that may be barely perceptible at the site can generate flash floods of extraordinary velocity and destructive power in the wadis that channel water through the archaeological zone. The Siq, through which all visitors enter and exit, is a primary flood channel. Ancient Nabataean dams and diversion channels, constructed specifically to manage this risk, were partially functional until relatively recently — their deterioration has increased the flood hazard. Modern drainage infrastructure has been improved following the 2018 deaths but requires continued investment.

Groundwater and Salt Damage — the most technically complex and in some ways most serious long-term threat. Modern water supply pipes serving Wadi Musa town and the tourism infrastructure have raised the water table within the sandstone mass that the monuments are carved from. As this moisture migrates through the porous sandstone and evaporates from carved surfaces, it deposits salts that crystallise and expand, causing progressive spalling of the stone. The faces of carved reliefs, the lower portions of tomb facades, and the internal surfaces of carved chambers are all showing damage of this type at rates that exceed natural weathering. Addressing the problem requires both repairing the leaking infrastructure and managing the groundwater levels that have already risen — a hydrological engineering challenge of considerable complexity.

Physical Weathering and Structural Stability — Petra's sandstone is inherently porous and susceptible to weathering from wind, rain, and temperature cycling. The carved surfaces that have survived two millennia are doing so because the site's climate is relatively dry and stable. Changes in rainfall patterns, increasing temperature extremes, and the physical disturbance generated by tourism activity are all accelerating weathering rates at margins that are measurable but have not yet been fully modelled.

Tourism Management — Jordan's economy is heavily dependent on tourism, and Petra is Jordan's most significant tourism asset. The economic incentive to maximise visitor numbers runs directly against the conservation interest in limiting visitor pressure on fragile sandstone surfaces, controlling the vibration from horse, donkey, and carriage traffic in confined spaces, and maintaining visitor management systems that protect the most vulnerable areas of the site.

Archaeological research at Petra has expanded significantly over the past three decades, driven by both the scientific interest of the site and the management need for baseline data on monument condition. The Brown University Petra Archaeological Project, the German Archaeological Institute, and numerous other institutions have conducted systematic excavation, survey, and documentation work that has substantially advanced understanding of the Nabataean city's urban planning, hydraulic systems, and cultural connections.

The hydraulic research has been particularly revealing. Detailed mapping of the ancient water system — channels cut into cliff faces, terracotta pipes running under street surfaces, cisterns carved from the living rock, dams placed across wadis to catch flood water and divert it to storage — has established that the Nabataeans were solving the same water management problems that now threaten their monuments, and that their solutions were often more sophisticated than the modern infrastructure that has displaced them. Research into the condition of ancient cisterns and channels has identified specific elements of the original system that could be restored to improve water management at the site.

Conservation science research — examining the mechanisms of salt crystallisation damage, the condition of carved surfaces across the monument inventory, and the effectiveness of different consolidation treatments — has produced the technical basis for intervention strategies that are being implemented at the site with partial success. The fundamental challenge is scale: Petra has hundreds of monuments, each presenting its own specific conservation challenges, and the resources available for systematic treatment are limited relative to the scale of the need.

The Treasury will not collapse. Its cliff face is structurally sound, and its lower portions are monitored carefully. The risk at Petra is not the loss of the most famous monuments but the gradual degradation of the carved surface detail — the reliefs, the decorative elements, the inscriptions — that carries most of the cultural and historical information the monuments contain. Salt damage, in particular, operates at exactly the scale that destroys this detail: not the collapse of structures but the progressive loss of carved surfaces, millimetre by millimetre, until the specific imagery and epigraphic record they carry is gone.

The flash flood risk, made devastatingly concrete by the deaths of 2018, is also a governance question as much as an engineering one: the decision to allow visitors into flood channels during warning conditions, the adequacy of early warning systems, and the visitor management protocols that govern behaviour in high-risk weather are all areas where policy choices determine outcomes as much as physical infrastructure does.

Petra has survived two thousand years, a major earthquake, the collapse of the trade system that built it, centuries of abandonment, and the displacement of the community that informally maintained it. It has survived all of that because the sandstone it is carved from is extraordinarily durable and the desert climate that surrounds it is extraordinarily dry. Neither of those protective factors is permanent. The question of whether the conservation and management systems being built around the site can match the quality and durability of the original construction is one that the next several decades will answer.