Bird's eye view of history

Mediterranean weather conditions are not the only reason that 2006 has been a particularly important year for aerial archaeology: this year also marks the centenary of aerial archaeology in Britain. An image over Stonehenge taken from a hot-air balloon in 1906 showed how even subtle earthworks could be identified and more easily analysed from above. Developments during the two world wars in aircraft, camera and film technology allowed the RAF to photograph almost all of the country as part of its national survey in 1946 and today, aerial archaeology plays an important role in gathering clues about Scotland's history.

"Aerial archaeology is quicker and more cost-effective than an excavation," says Dave Cowley, an aerial survey manager with the Royal Commission on the Ancient and Historical Monuments of Scotland. "It allows us to look at the broader picture and gives us an overview of the whole ground plan. When the information is used in conjunction with more detailed investigations, it can give us quite an accurate picture of what life was like hundreds or thousands of years ago. [This year] has been a wonderful year for aerial archaeology, and we may not see another like it for a decade. A prolonged period of hot, dry weather provides ideal conditions for [us].''

Archaeological sites become visible most commonly on farmland during the summer months. "In the lowlands, in particular, ancient sites and monuments have been levelled out by agriculture, and while these sites are not usually detectable, during hot spells they can become visible from the air," says Cowley. "When cereal crops are planted on the top of these sites, different rates of growth and ripening can cause buried features to reveal themselves. Crops will often grow taller and greener above ancient ditches because extra water and nutrients are found there, while buried walls or paths can deprive plants of nutrients, showing up as yellow patches, known as parching."

Because of the farming calendar, archaeologists face a race against time to get all the information catalogued. "We have to conduct all our investigations [by] August, as we have to photograph as many sites as possible once the crops have come up, but before they are harvested," says Cowley. "The sites are no longer visible and won't be until the next spell of hot weather. Sites become visible most commonly among cereal crops in fairly well-drained soils that have been cultivated, but can occur under grass as well. If you've ever had a path in your garden that's been covered over with grass, for example, you might notice that in summer, buried details of the path show through."

Many of Scotland's archaeological sites have been photographed from the air over past decades, but the key development this year is the increased level of detail that has become visible. "Sites become visible every summer to varying degrees, but for the past few years we have had fairly poor summers," says Cowley. "This year, ideal conditions meant that sites became visible of which we had been completely unaware, including a prehistoric settlement near Melrose, and an Iron Age enclosure at Letham. In addition, existing sites have appeared in much greater detail. This was particularly pronounced at the Roman forts and camps at Newstead, where stone walls have become much more visible, and we are now seeing traces of gate towers that we had never seen before. It became much easier to make out the internal layout of the fort and the images gathered should tell us a lot more about the lives of the people who lived there.

"The information will now have to be analysed thoroughly and will be made available to the public on the Canmore Database. This is [what] gives future generations access to information and records on every aspect of our built environment. We can only speculate at the moment as to what this year's findings may tell us, but one key thing is that we have discovered more Iron Age locations.

"This is an area where our information is patchy, so hopefully we will be able to add a few more pieces to the puzzle. It has been a fantastic summer: I hope that our discoveries will allow us to fill some gaps in our knowledge."

• View the Canmore Database at www.rcahms.gov.uk

From the air

Newstead

Roman forts and camps at Trimontium (Newstead) which lie beneath the Eildon Hills near Melrose. Although the site has been excavated, aerial photography this summer has revealed new details including stone walls and a gate tower.

Redpath

A large, heavily defended prehistoric settlement at Redpath, near Melrose, is thought to be around 2,000 years old and was recorded for the first time this year.

West Lindsaylands

Possible remains of an Iron Age fort at West Lindsaylands in South Lanarkshire. Two arcs of ditches in the top right of the field may be the remains of a Neolithic enclosure and an Iron Age fort. A combine harvester is harvesting the crops in this aerial photograph.

Letham

This circular enclosure at Letham in Fife was recorded for the first time this year and is likely to be Iron age or earlier.

Crail

Second World War airfield at Crail in Fife. Buildings and paths that have been removed are visible as crop marks above the buildings still standing. Extra details, including paths and walls, have become visible for the first time.