Not all forms of communication are based on speech or writing. Just as the Inca encoded information in strings and knots known as quipus, and the inhabitants of the Marshall Islands created intricate navigational charts from sticks and seashells, the Aboriginal peoples of Australia developed their own sophisticated means of transmitting information across vast distances. Known as message sticks, these small carved pieces of wood, rich in symbolism, served as important tools of communication between different communities.

An early 20th century Aboriginal message stick, almost a meter in length, made of extremely dense hardwood, and with ochre coating message on both sides. Credit: Carter's

On 9 October 1917, during the Third Battle of Ypres, a battalion of Australian soldiers entered a place known as Celtic Wood, near Passchendaele in West Flanders, Belgium, to attack German positions. Most were never seen again. Of the 85 men to raid Celtic Wood, just 14 made it back to their lines. The rest vanished without a trace. The fate of the lost battalion has remained one of the greatest enigmas of Australia's Great War.

The battlefield in Poelcapelle, Belgium. Credit: Wikimedia Commons