For centuries, historians and archaeologists have puzzled over the many mysteries of Stonehenge, a prehistoric monument that took an estimated 1,500 years to erect. Located on Salisbury Plain in southern England, it is comprised of roughly 100 massive upright stones placed in a circular layout.
First, Neolithic Britons used primitive tools, which may have been fashioned out of deer antlers, to dig a massive circular ditch and bank, or henge. Deep pits dating back to that era and located within the circle may have once held a ring of timber posts, according to some scholars.
Several hundred years later, Stonehenge’s builders hoisted an estimated 80 bluestones, 43 of which remain today, into standing positions. These stones have been traced to the Preseli Hills in Wales, some 300 kilometres from Stonehenge.
According to one long-standing theory among archaeologists, Stonehenge’s builders fashioned sledges and rollers out of tree trunks to lug the bluestones from the Preseli Hills. More recent archaeological hypotheses have them transporting the bluestones with supersized wicker baskets on a combination of ball bearings and long grooved planks, hauled by oxen.
As early as the 1970s, geologists have been adding their voices to the debate. Challenging the classic image of industrious builders hauling giant stones from faraway Wales, some scientists have suggested that it was glaciers, not humans, that carried the bluestones to Salisbury Plain.
The third phase of construction took place around 2000 BCE, when sandstone slabs known as ‘sarsens’ were arranged into an outer crescent or ring. Radiocarbon dating has revealed that work continued at Stonehenge until roughly 1600 BCE.
But who were the builders of Stonehenge? In the 17th century, archaeologist John Aubrey made the claim that Stonehenge was the work of druids, who had important religious, judicial and political roles in Celtic society. However, radiocarbon dating later demonstrated that Stonehenge stood more than 1,000 years before the Celts inhabited the region.
While there is consensus among the majority of modern scholars that Stonehenge once served the function of burial ground, they have yet to determine what other purposes it had. In the 1960s, the astronomer Gerald Hawkins suggested that the cluster of megalithic stones operated as a form of calendar, with different points corresponding to astrological phenomena.
Urban farming is not, of course, a new phenomenon. Inner-city agriculture is booming from Shanghai to Detroit and Tokyo to Bangkok. Strawberries are being grown in disused shipping containers, mushrooms in underground carparks. Aeroponic farming, he says, is 'virtuous'. The equipment weighs little, can be installed on almost any flat surface and is cheap to buy: roughly 100 to 150 per square metre. It is cheap to run, too, consuming a tiny fraction of the electricity used by some techniques.
Produce grown this way typically sells at prices that, while generally higher than those of classic intensive agriculture, are lower than soil-based organic growers. There are limits to what farmers can grow this way, of course, and much of the produce is suited to the summer months. 'Root vegetables we cannot do, at least not yet,' he says. 'Radishes are OK, but carrots, potatoes, that kind of thing - the roots are simply too long. Fruit trees are obviously not an option. And beans tend to take up a lot of space for not much return.'