Beyond the reach of regulation are accidents - long may they live.

Cities have become a cause celebre among urbanists the world over, scaling ever new heights of hyperbole in industry and political adulation. The management and planning of cities – once left largely to market forces – is now recognised as a field of specialist expertise, requiring extensive regulatory intervention. This has spawned the global careers of any number of speakers whose main job, it seems, is to lecture rapturous audiences of city planners, developers, political and policy leaders on the best ways to manage and grow their cities for sustainability, liveability and resilience, among other things.

The language of cities and their management has similarly evolved in recent history. No longer does city management mean a local government focus primarily on "rates, roads, and rubbish" – cities are now described as "complex ecosystems" or "living organisms" with a "metabolism" all of their own. Some of them are "smart" and "intelligent" and all of them we are told – like a collection of fine arts – need to be carefully "curated."

Urban design and city management is accordingly becoming more meticulously studied, planned and stage-managed than ever before. Spurred on by forecasts that half the world's population will soon be living in cities (mostly - as it turns out - in the suburbs of those cities) the pressure is on for city planners to deliver growth without sacrificing amenity or delivering lower standards of living or quality of life than previous generations. This is a challenge of Sisyphean proportions.

Ironically however, many of the qualities of cities and the celebrated places within them now enjoyed by many were not the result of carefully managed or planned urban development, but accidents of history. 18^th and 19^th Century urban growth in the US, Europe and Australia revolved around industry – well described in Eric Hobsbawn's classic "Industry and Empire." Rivers were for the transport of goods to cities where wharves were constructed and where factories sprung up. Rail was mainly (in many centres) for freight. Power stations, goods yards and industrial lands were developed around these transport connections. Workers lived in cramped and unhealthy conditions close to these places of industrial employment because their form of commuting was mostly walking or - if lucky - by austere and perfunctory public transport.

While no city experienced the same patterns of growth or the same economic drivers, many did enter the 20th century with legacies of their past in the form of housing, industrial, administrative and transport systems which were largely developed without the careful supervision of today's modern urban planner. Post-war prosperity in the mid-20th Century heralded for many the move away from cramped inner-city housing to new, expansive and healthier suburban domains. Older style industries and work practices changed, many moving to newer transport facilities such as modern seaports, airports and intermodals, or to other more convenient locations. Some shut down altogether: the collateral damage of industrial and technological change.

Both residents and businesses left behind a legacy of mostly accidental urban development. And ironically, it's that very accidental quality of urban development and built form heritage which many cities now seek to protect - through various preservation laws, via support of adaptive re-use (finding new ways to use old buildings designed for a different purpose altogether), or via attempts to emulate that accidental quality in prescribed regulation.

There is a paradox in this. It was the very lack of regulation that helped make many places or buildings or urban features worthy of preservation. Think of the inner-city terrace houses of Sydney, Australia, once home to the working poor. Or the timber and tin workers' cottages of Brisbane, Australia – built from the only readily available (and low cost) materials at the time. These are now highly prized – not just for their location but also their typology and heritage qualities.

A similar story can be told in many cities which now celebrate converted warehouses, factories, hospitals, ports, and even power stations. These structures weren't the result of careful planning but originally designed and located out of necessity and opportunity. Many are now prized community assets, accommodating entirely different activities to their original design.

Similarly, in modern cities there are places that are praised as clusters of cultural, ethnic, social, artistic or community value. Places where people gather willingly, but in way that wasn't planned - it just 'happened.' Think of the haphazard laneways of Melbourne's inner city or the many cultural, food or entertainment centres which have sprung up not because they were planned, nor were they encouraged, but because they escaped the watchful eye of regulators or over-zealous inspectors. Having secured their place in the life of the city (by virtue of their popularity), their "accidental" existence isn't just condoned but celebrated. The same can't be said for the carefully managed environments of the modern shopping mall which - although commercially successful - are unlikely to ever reach the same levels of community adulation or sentiment.

Could a rule book of building codes, access, regulatory and other permissions foster planned urban creativity in the same way as the accidental outcomes? Perhaps not. The work of the artist Banksy isn't legal or officially sanctioned. But his works are highly prized. They are accidents of urban life incapable of official emulation of recreation. There's only one Banksy.

None of this is to suggest that a well-managed urban environment can't be "curated" to support a range of positive urban outcomes. Modern urban planning is fast evolving and many technologies in particular are giving urban planners and city managers new, highly advanced tools to understand how the community uses their urban spaces, and how to design places for even more positive outcomes. Nor does it suggest that the absence of regulation is the answer to anything. Unregulated urban development in the manner that early cities developed would invariably lead to regrettable outcomes – environmentally, socially and economically.

But we need to remind ourselves of the limits of regulation and prescription. There are forces at work which in the evolution of cities that can still be left to accident, by ensuring we don't become overly prescriptive.

"Accidental cities" is used in some quarters as a derogatory term or as a tale of caution. Failing to meticulously plan every detail, we are warned, leads to inefficiencies and to cities not performing at their peak. But leaving room for accidents is also important. The surprise start-up hub. The surprise retail success story working from a location no one thought credible. The artists, foodies, businesses and industries adapting faster to new technologies than any set of planning regulations could possibly keep pace with.

There is a difference between the real and the reconstituted. We can tell the difference, without really thinking about it. For cities to remain real, it could be wise to recognise the limits of their "curation" at the hands of experts. There are places beyond the reach of regulatory control where accidents could – and should – be encouraged to continue to happen.