By Hugh O'Shaughnessy
BBC News, Brazil
Police have taken to an unusual form of locomotion in the Brazilian city of Belem.
The mounted police look splendid on their animals.
The buffaloes are regularly called out on police duty
Calm, dignified and, yes, friendly, they glance down indulgently on us visitors to the international fair in Belem.
Belem - whose name is the Portuguese form of Bethlehem - is the capital of the Brazilian state of Para and it lies near the mouth of the Amazon.
But, if anything, the police animals look even calmer, more dignified and friendlier than their riders, a real credit to the force. Altogether a fine body of men and beasts, you would say.
Sadly, it is not often that full marks can be given to the guardians of the peace in Brazil.
Under the military dictatorship which seized power in 1964, the police were often guilty of the greatest torture and cruelty.
Their senior officers generally escaped punishment because the Brazilian regime was fallaciously presented as the "good guys" in the Cold War.
But, for a long time, Brazil's constabularies never reached the minimum qualification for any police force - namely that it caught more criminals than it employed.
'A giant's bicycle'
The dictatorship is, thank goodness, long over. But there is still a taint of police excess in many spots in this enormous country.
These men, benignly guarding us on their mounts on the banks of the Amazon, are something other.
Perhaps it is because they are carried not on excitable horses, but on placid buffalo.
The buffaloes' muscled flanks shine.
Their horns, which have a span of a metre and a half, hang down impressively for all the world like the drop handlebars of a giant's bicycle.
And they have all got names.
Xodo (which means "my treasure" in Portuguese) and Carolina, for instance, are patiently yoked together to a wooden cart.
There a constable stands proudly grasping a ceremonial lance from which the force's pennant stirs lazily in the damp night air.
The buffalo can go into action with vehicles and are regularly called out on duty with the fire service. They are always ready to trot off to help douse a blaze in some thatched hut or drag a car out of the Amazonian mud.
In fact they do not usually parade here in Belem at all. They are stationed across the river in the mud of Marajo, an island the size of Switzerland in the Amazon delta.
I will appreciate my mozzarella even more when I eat it and I will certainly never order a buffalo steak in any Brazilian restaurant
Marajo lies where the world's greatest river - 4,000 miles (6,000 km) long - empties into the Atlantic.
The Amazon is 12 times greater in volume than the Mississippi at New Orleans and more water flows by Marajo every day than the Thames carries past the House of Parliament in London in a whole year.
Buffalo were introduced from Africa in the 1930s to produce milk for mozzarella cheese, meat and hides and they bred successfully.
They also took to the swampy terrain better than mere horses whose hooves rotted disastrously in the wet.
The hooves of the buffalo are more like steel than like the horn of other quadrupeds and are splayed out more widely.
That enables them to work with dignity and aplomb in conditions which would have crippled horses.
A demanding art
They have also got another recommendation that is particularly useful on Marajo, a land noted for the prevalence of its snakes such as boas and rattlesnakes.
Unlike the delicate, humped zebu cattle, the buffalo are amazingly thick-skinned.
"Any snake which tried to sink its fangs into a buffalo, would certainly come off second best. It would be in urgent need of a dentist," says my friend Dutra, a teacher in one of the Belem universities.
So, a few decades ago, the authorities decided to call the buffalo in for police and fire service duty and a score or more of them are today quartered in Soure, the main town on Marajo.
Their riders have clearly got good relations with them, guiding them gently on their way with reins attached to a ring in their nose.
This gives the beasts something of a pained look, their great eyes cast upward in that spirit of longsuffering often to be glimpsed in Italian renaissance paintings of early Christian martyrs.
But they never, it seems, lose their phlegmatic outlook on life.
The other day at the show in Belem the police were happy to pose with the children of visitors on the buffalo saddles, for the parents to take photographs.
The constables handled the youngsters with gentleness and patience, qualities which they surely picked up from the buffalo. (These traits are not, it must be said, usually associated with Brazilian police, mounted or on foot, uniformed or in plain clothes).
Riding the broad-backed buffalo is a demanding art, my Brazilian friends told me.
"It's a bit like riding a camel and it places no little strain on your upper thighs, if you're not used to it," one recounted.
For my part I have been powerfully affected by my recent encounter in Belem.
I will appreciate my mozzarella even more when I eat it and I will certainly never order a buffalo steak in any Brazilian restaurant - or any other restaurant for that matter.
After all, it could have come from Xodo or Carolina or one of their offspring and that would never do.
From Our Own Correspondent was broadcast on Thursday, 29 June, 2006 at 1100 BST on BBC Radio 4. Please check the programme schedules for World Service transmission times.