Tyres' Arrow

Tyres' Arrow is the first survey mark on Australia's fist surveyed state border. 

Charles James Tyers was a navigator and colonial surveyor who conducted the first survey to fix the approximate boundary between New South Wales (now Victoria) and South Australia in late 1839. Under orders from Governor Sir George Gipps, Tyers used three distinct methods—triangulation from Melbourne, chronometric measurement from Sydney, and lunar observations—to determine the location of the 141st Meridian of East Longitude at the mouth of the River Glenelg. Despite the technical challenges of the era, he successfully fixed the longitude in the field to within approximately 480 meters (20" of arc) of its true position.

The critical reference point for this survey, which became known as "Tyers' Arrow," was established on December 16, 1839. Located on a low sand dune approximately five chains (100 meters) north of the coast, Tyers marked the boundary by packing limestone into a hole three feet long and one foot deep in the shape of a broad arrow. From this starting point, he extended a "true north line" marked at one-chain intervals with smaller limestone-filled holes across the River Glenelg basin and into the thick forest beyond.

This limestone arrow served as the foundational benchmark for subsequent border surveys. In 1847, Surveyor Henry Wade located the arrow and used it to calculate the final position of the border, eventually setting off a distance to the west to commence the formal survey of the boundary between the provinces. Although the mark was seen again in 1911 during a High Court dispute over the border's location, it subsequently disappeared from history until a modern search in 2001 successfully relocated a pile of limestone rocks in a sandy hollow matching Tyers' original coordinates.