What is the point of circumnavigating the world along a line most of us only know from fading memories of geography lessons?
By Simon Reeve
Presenter, Tropic of Capricorn
Travelling the world along any line will throw up unexpected adventures and stories, and the random nature of this journey offered me unique insights into the southern hemisphere.
The Tropic of Capricorn is one of the five major circles of latitude
Capricorn cuts through Namibia, Botswana, South Africa, Mozambique, Madagascar, three country-sized regions of Australia (Western Australia, the Northern Territory and Queensland), then Chile, Argentina, Paraguay and Brazil, where my adventure ended on the Atlantic coast.
Following the line took me to stunning areas of the world, but it was also a chance for spontaneous discoveries about our changing environment, poverty, globalisation, AIDS, the rise of the Chinese economy, and the suffering of Africa.
But Capricorn is much more than just a random line, or an imaginary mark on a map.
Band of life
The line is actually the most southerly latitude at which the sun can appear to be directly overhead which occurs at the summer solstice, just as it does on the Tropic of Cancer in the northern hemisphere.
As such, map-makers identify Capricorn and Cancer as the southern and northern boundaries of the tropics, a region of huge political and environmental importance for the planet, with a climate that drives the ecosystem of our entire world.
Simon standing at the Tropic of Capricorn in Namibia
Half the surface of the planet is in the tropics.
Between Capricorn and Cancer is a band of life 3,222 miles wide, a home to extraordinary natural biodiversity, but also an overwhelming concentration of human suffering.
Outside the tropics every country in the temperate zone has either middle or high income economies.
Researchers at the Harvard Centre for International Development identify only three tropical economies, Singapore, Hong Kong, and part of Taiwan, as 'high-income'. Even in states straddling a line of the tropics, such as Brazil and Australia, wealth is concentrated in the temperate areas.
A greater challenge
I fell in love with the sultry, sweaty tropics when I passed through the middle of the zone while following the Equator for the BBC in 2006. For my next journey I hoped to learn more about life in the remote parts of countries on the southern edge of the tropics.
In setting out on this journey we had the experience of travelling around the Equator to call upon.
But this was a longer journey and a greater challenge.
A quick glance at an atlas shows the demands of the journey.
Capricorn passes through the Namib desert, the Kalahari, the Australian outback, the Andes - all tough environments.
But during the second half of 2007, after much preparation, I set-off on four trips around Capricorn, each a gruelling month-long shoot.
Travelling almost the entire journey with me was Brian Green, the hardy South African cameraman whose energy and sheer dynamism was essential for bringing the humour, spontaneity, and sense of adventure to the screen.
Each leg of the journey had a different director, to bring a new pair of eyes to the project.
From the beginning the idea was to use Capricorn as a guide, but not a straitjacket.
The Wichi are struggling to get legal recognition for the land they own
The point of the journey was not to obsessively track Capricorn, but to look for fascinating places and people near the line on the southern edge of the tropics.
By zigzagging along the line we could, for example, visit the Wichi people of northern Argentina, hunting for wild honey and witnessing how their ancient way of life in Hoktek T'oi is under threat.
Searching for stories
This is not a series that focuses entirely on the rigours of the journey.
The people we met and the stories we heard are more interesting than watching hours of me fixing punctures or complaining about my stomach bugs. So we had to be careful about how much time we spent in uninhabited wilderness, of which there are vast tracts on Capricorn.
When we did cross a wilderness it was usually because we were looking for something, or someone.
So in Botswana we drove for three days across the heart of the Kalahari in search of the San Bushmen.
At the entrance to the Central Kalahari Game Reserve we were told our cars were the first vehicles to pass that way for two years.
We very nearly did not make it to the remote Kalahari settlement of Metsiamanong, as the sucking sand ate our food, time, and supplies.
I travelled by car, boat, train, plane, horseback, and motorbike along the Tropic of Capricorn during more than 120 days of filming.
Each country had at least one fixer, a local guide, most of whom are featured in the programmes.
So while there were only four people, including me, in the crew it took more than 30 people to bring this epic journey to the screen. Far more if you count the local drivers and technical staff back in London.
I hope you think it was worthwhile.
Presenter: Simon Reeve