THE archaeological site in Thonotosassa, which means “land of flint” in the Seminole-Creek language, is nothing much to look at: a few pits dug in the sandy soil among gnarled live oak trees, with cattle grazing round. No one guards it. Yet this place, about 17 miles (27km) north-east of Tampa, is a good spot to find Indian artefacts, on high ground close to fresh water. Robert Austin, an archaeologist who has dug there often, says that some of the remains discovered date back 12,000 years.

The chance of finding ancient objects draws thieves, too, to dig for arrowheads, flints and pots. A good arrowhead can fetch thousands of dollars. Trespassers usually scout the scene of the would-be crime during daylight hours, then return with shovels at night. No one stops them.

Last month five men were arrested at Thonotosassa on suspicion of intending to loot it. They said they were collectors, and had no intention of selling the arrowheads they were looking for. They have now been charged with trespassing.

The problem is not confined to one area of the country, or even to the open air; 26 bowls and bottles of the Caddo Nation, about 600 years old, were stolen from Southern Arkansas University in August 2006. But lack of security at Indian archaeological sites makes them particularly vulnerable.