The male and female were released into a 15 hectare fenced area making it the second licensed release of the mammal by the conservation charity in the last 15 months.
Jane Cecil, National Trust general manager for the South Downs, said: “We’re delighted that such a ground-breaking moment has been reached after a lot of hard work and preparation.
"We’re really grateful to the Black Down and Hindhead Supporters of the National Trust. Their generosity – and that of our local community – raised some £62,000 so that the project could go ahead. We feel very fortunate to have this remarkable support, alongside a grant from Viridor Credits Environmental Company."
Having once been an important part of the ecosystem, beavers became extinct in Britain in 16th century because of hunting for their fur, meat and scent glands.
The release is part of the charity’s ambitions to create priority habitats for nature and to increase the diversity of species and wildlife on the land in its care.
David Elliott, National Trust lead ranger for the South Downs West, said: “Today we are reintroducing a species which has been absent from this landscape for the last 400 years. Beavers are nature’s water engineers, they can help bring back the natural processes that have been missing from our environment.
“By creating their dams, the beavers will create new and wildlife-rich wetlands; ponds, rivulets and boggy areas that will, over the next few years, benefit a range of wildlife including amphibians such as frogs and toads, many dragonflies and damselflies and wildflowers such as Devil’s-bit scabious that love damp meadows.
“They’ll help us create a pyramid of life based on wetlands – including bird and bat species as their prey increases in abundance.”
The beavers were re-located from wild populations in Scotland, under licence from NatureScot, by consultant ecologist Dr Roisin Campbell-Palmer. Health screening and pre- release care has been provided by Five Sisters Zoo in West Lothian.
A growing number of sites in the British Isles have reintroduced beavers.The National Trust’s South Downs programme will be carefully monitored for its benefits: from water quality and floodwater management to ecology and vegetation changes, by research partners at Imperial College London, the University of Birmingham and the University of Exeter.
Bob Daniels, chair of the Black Down and Hindhead supporters, said: “The project is a great example of the things we can do locally to positively influence species decline, in a world where the opposite is an alarmingly prominent feature of global headlines.
"Thanks to local donors, large and small, and several years of hard work the beavers have arrived on site. Now it’s up to the beavers to continue that hard work as ecosystem engineers in residence.”