An accidental discovery
In 1902, construction workers cutting a cistern for a new housing development in Paola, Malta, accidentally broke through the roof of an unknown subterranean structure. Initially, they tried to hide the discovery to avoid halting their work. What they had stumbled upon was the Ħal Saflieni Hypogeum, a massive Neolithic complex carved from soft Globigerina limestone. The structure descends three levels deep and covers about 500 square meters.
Archaeological work, which began in earnest under Sir Themistocles Zammit, revealed that the Hypogeum was constructed between 4000 and 2500 BC. The builders used only tools of flint, obsidian, and animal bone to hew the labyrinthine halls and chambers from the solid rock. The site was both a sanctuary and a necropolis; the remains of an estimated 7,000 people were found within its walls. Some chambers feature red ochre paintings of spirals, polygons and animal figures—the only prehistoric paintings ever found on the Maltese islands.
The science of sound
The Hypogeum's most scientifically intriguing feature is its acoustics, particularly in a chamber on the second level known as the "Oracle Room". Archaeoacoustic studies have detected a strong double resonance frequency here, with peaks around 70 Hz and 114 Hz. A male voice speaking or chanting at these low frequencies can create a resonant effect that is felt physically throughout the complex. Some sounds have been recorded echoing for up to 13 seconds.
This specific acoustic property has led to scientific investigation into its potential effects on the human brain. EEG studies have monitored the brain activity of volunteers exposed to similar frequencies. A 2008 study found that at 110-111 Hz, brain activity in the language centers decreases, while activity patterns shift from the left to the right hemisphere—a change associated with intuition, creativity and emotional processing. This frequency appears to uniquely induce a mental state similar to that experienced during meditation or at the edge of sleep. While it is impossible to know the builders' intent, the precise acoustic properties suggest an understanding of sound and its psychoactive effects.
Among the many artifacts recovered was a small clay figurine known as the "Sleeping Lady," found in one of the Hypogeum's pits. The detailed figure depicts a woman with large hips lying on her side on a couch. Its meaning is unknown, but theories suggest it represents sleep, death or a mother goddess figure.