Fond hopes that ancient Britain enjoyed a golden age of peace before Roman and other invasions have been shaken by a gruesome discovery in a Derbyshire hill fort’s defensive ditch.

For the first time in the UK, archaeologists have found carelessly-buried iron age skeletons which suggest a selective massacre of women and children.

The tumble of scattered bones has come as a surprise to those taking part in one of the biggest community digs in recent British archaeology.

More than 400 schoolchildren joined specialist archaeologists and local volunteers to research Fin Cop in the Peak District, which dates from between 440BC and 390BC.

The finds include the skeleton of a pregnant woman crushed beneath a collapsed stone wall, one of a number of defences which appear to have been built hastily before some kind of catastrophe.

The remains of a teenage boy were discovered huddled at the bottom of the ditch, along with seven more skeletons, all women or children.

Dr Clive Waddington, who directed the two-year dig for Archaeological Research Services, said: “In recent years there has become an almost accepted assumption that warfare in the British iron age is largely invisible.

“Hill forts have been seen as displays of power, prestige and status rather than places with a serious military purpose.

“The gruesome discoveries at Fin Cop have reopened the debate on the purpose of hill forts. For the people living here, the hurriedly constructed fort was evidently intended as a defensive work in response to a very real threat.”

The strength of the theory depends in part on further excavations yet to be completed, with only 10 metres of the 400 metre-long ditch so far investigated.

Team members believe the remains of hundreds more victims may lie in the neighbouring stretch.

There could be gentler explanations for the deaths: none of the nine skeletons show signs of violence, suggesting death would have been from flesh wounds or suffocation – or possibly disease.

Explanations could include a disastrous plague or the punishment of a household by the rest of the community.

The absence of adult male remains in the ditch is also a puzzle, especially as traces of cattle, sheep and pigs were found, along with horse bones, which suggest that Fin Cop’s inhabitants included people of high status.

Archaeologists are now debating whether men might have been enslaved or pressed into military service by the victors in a battle.

The absence of similar finds at other British hill forts may be due to geology – animal remains decay more slowly in Fin Cop’s limestone than in the sandstone which underlies most other significant sites.

But Jon Humble, English Heritage inspector of ancient monuments for Derbyshire, said: “There are many more mysteries out there in the Peak District that have yet to be solved.”

Local people, who provided more than 100 volunteers for the dig, are keen to find out more.

Ann Hall of Longstone history group said: “Locals have always viewed the hill as a peaceful spot. Now we have uncovered sad evidence of an ancient massacre and learned that our well-loved landmark may also be a prehistoric war grave”.