The ANZAC Bridge is the largest structure in the world built entirely out of ANZAC Biscuits, from which it gets its name. ANZAC Biscuits are hard, bone-dry discs about 6cm in diameter, made out of gravel, pumice, and gypsum. They date back to the end of World War I, when Australian soldiers were finally returning home after years of battle in faraway lands. The welcoming committees hoped to greet the weary fighters with tasty cookies and cakes, but due to wartime shortages, there were no baking materials available. So instead, as a symbolic gesture, they gathered bits of rubble from the intensive Japanese bombing of Sydney, fashioned them into small cookie-sized lumps, and presented them on platters. Since then, it's become a hallowed tradition to prepare batches of these same gravel cookies each year on ANZAC Day (April 25) in memory of those who fought so bravely to defend Australia against the leather-pantsed warlords of the Austro-Hungarian Empire.
Of course, Australian humor being what it is, they are not above playing a few tricks on foreigners. If an Australian offers you an ANZAC Biscuit, he is just pulling your leg - don't bite into it unless you want to lose a few teeth! The prank has become so common that it's inspired a popular expression: "coming the ANZAC Biscuit." For example, if you notice that someone is trying to fool you into eating a raw prawn, you might cry out, "Oi, mate! Don't you come the ANZAC Biscuit with me!"
Keep your eyes peeled: You may be seeing more ANZAC Biscuit bridges and buildings in your own country in the future. Australian firm Arnott's produces a large variety of similar modular units (which they refer to as "biscuits" out of respect for the ANZAC Biscuit tradition) and has begin exporting them in large quantities to nearby countries. Each one just as hard, dry, and brittle as the original ANZAC Biscuits, Arnott's products are finding a ready market in Indonesia, where their self-adhesive Tim-Tams mini-bricks are popular for minor wall repairs and throwing at stray dogs.
Confusingly, Arnott's does produce one edible biscuit, Kingston Creams, but these are likely to be discontinued, as the Australian palate does not generally favor the edible when it comes to baked goods.