Out in the flat, featureless bush, on the outskirts of Francistown, near the Zimbabwean border there is a bleak Botswanan prison.
By Barnaby Phillips
BBC, Southern Africa
It is a collection of brick houses surrounded by high fences topped with barbed wire.
The influx of Zimbabweans is worrying Botswana
But it is clean and, so far as I can tell, a humane place.
It only opened in 2002, specifically to host illegal immigrants.
There are people from all over Africa here - the Democratic Republic of Congo, Somalia, Rwanda. But, above all, there are Zimbabweans.
Very few of them are political activists appealing for asylum.
They are simply ordinary people - men and women - ruined by their country's economic collapse, who came to Botswana to try and find work, and perhaps even send a bit of money back home.
On the day I visited, there were 300 Zimbabweans in custody.
"You should have been here in December", one official told me.
"We had a big round-up of illegal foreigners in Francistown, and we brought in more than 4,000 of them."
On an average day, the Botswanan immigration authorities load about 100 Zimbabweans onto trucks, and drive them back to the border.
Its an expensive, and probably futile exercise. Because all of the Zimbabweans I spoke to said that they would try and come straight back to Botswana.
"In Zimbabwe there is just corruption.
And there are no jobs. So of course I will come back; do you expect me to starve?" asked one.
Many of the Zimbabweans are just teenagers - their young lives destroyed by events back home.
One 16-year-old said: "My father was the foreman on a farm - but he lost his job - and then he could not afford to send me to school. So I came to Botswana, because here the currency is strong".
The Botswanan prison staff sympathise with the Zimbabweans.
"We have to do our job and expel those without papers. But of course we know why they come here. Life over there is too hard," said one official.
And he pointed to a thin teenage boy getting on board the truck which is bound for the border.
The political stalemate in Zimbabwe has fuelled the crisis
"That one has been here three times already this month."
Zimbabwe's crisis is affecting all of southern Africa, and neighbouring Botswana is on the frontline.
Botswana has a small population - less than 2 million - and it is a tightly-knit, conservative society.
Now it is feeling overwhelmed by the influx of Zimbabweans.
"There are now more Zimbabweans in Botswana than there are Batswana", one government official told me.
She is wrong, of course, but the sentiment that Botswana is being swamped is a common one.
Locals now refer to one part of the capital Gaborone as "little Harare" because of the dozens of Zimbabwean men and women who line the roads, begging passers-by for odd jobs, or "piece-work" as they call it.
In a village outside Gaborone I met local chiefs who are not happy with the arrival of so many outsiders.
"They rape, they steal, they cut people with knives", one old chief told me, pointing to a group of Zimbabweans sitting under a tree.
"We never used to have these problems" he said.
Driving back to Francistown, we were given permission to visit the fence which the Botswanan government is building along its border with Zimbabwe.
By the time it is completed, probably later this year, it will run for 300 miles. Eight-feet high, and with an electric current on top, its costing the Botswanan government about £2m.
It is a delicate issue.
Botswana is building a fence at its border with Zimbabwe
Zimbabwe's High Commissioner in Gaborone has complained that the Batswana are trying to build an African "Gaza Strip".
But the Batswana insist the fence is designed to stop animals, not people.
"It's all to do with foot-and-mouth disease. We've had two outbreaks in recent years, and we can't afford another one," one agricultural official told me.
Botswana exports its beef to the European Union and lucrative contracts have been disrupted by the outbreaks.
The Batswana suspect that on both occasions the disease came from Zimbabwe, where commercial cattle ranching has collapsed, and the movement of animals is no longer carefully controlled.
So the fence ought to keep Zimbabwe's animals out of Botswana.
But it will, no doubt, make it harder for many Zimbabweans to escape their country's tragic decline.