An underground economy
Danebury is one of Europe's most intensively studied Iron Age hillforts. Excavations between 1969 and 1988, led by archaeologist Barry Cunliffe, investigated 57% of the fort's 5-hectare interior. The work uncovered evidence of roundhouses, rectangular buildings, and thousands of underground storage pits. These pits, dug into the natural chalk bedrock with iron adzes and mattocks, characterize the site.
The majority of the pits are circular, with many having a "beehive" shape—a narrow opening widening into a larger chamber below. This design was intentional, making the pit easier to seal. Archaeobotanical analysis of carbonized grains found within the pits shows the inhabitants grew specific cereal crops. These included spelt (Triticum spelta), emmer wheat (Triticum dicoccum), and six-row hulled barley (Hordeum vulgare). The number of pits shows a capacity for storing agricultural products far beyond the needs of the resident community, which is estimated to have been 300 to 400 people. This shows Danebury was a central storage and redistribution hub for a wider agricultural region.
The science of storage
The effectiveness of these chalk-cut pits lies in the principle of hermetic storage. Once a pit was filled with threshed grain, its narrow mouth was sealed with a plug of clay and chalk to make it airtight. Inside the sealed environment, natural biological processes took over. Respiration by the grain itself, along with bacteria and fungi, consumed the trapped oxygen.
This activity produced a high concentration of carbon dioxide, which created a self-sterilizing atmosphere. The anoxic, high-carbon-dioxide environment halted the process of decay, prevented seeds from germinating, and killed insect pests like grain weevils. Experimental archaeology at Butser Ancient Farm has confirmed the efficiency of this method, showing that grain can remain viable for consumption or as seed for years. The only spoilage occurred in a thin layer, just 1-2 cm thick, where the grain touched the pit walls. This spoiled layer could be fed to animals, leaving the bulk of the grain perfectly preserved. The subtle dips in the ground visible at Danebury today are the last surface traces of this sophisticated, centuries-old food security system.