The 3,178 km line was built in less than two years and joined on 22 August 1872.
It linked Australia to an undersea cable from Indonesia that came ashore at Port Darwin. The project was under the direction of Sir Charles Todd, KCMG, Superintendent of Posts and Telegraphs, South Australia.
Communication between Australia and the rest of the world could now happen in hours rather than months.
The first telegraph messages from overseas were received on 22 October 1872 via the undersea cable brought ashore on 7 November 1871.
Markers under this recognition are located in Darwin (near where the cable came ashore); at the Telegraph Station at Alice Springs (as marked on the map above) and at the General Post Office Adelaide. In addition there is a separate recogtnition of the joining of the wires of the Overland Telegraph near Warne Ponds between Newcastle Waters and Elliott. The marker is at a cairn on the side of the Stuart Highway 25 km south of the Dunmara Roadhouse. The pole where the wire was joined remains in the bush about 2 km west of the cairn.
An Oppenheimer metal pole carrying two wires (the second wire was added some years after commissioning of the line)
Source: State Library of SA 
Overland Telegraph wooden angle pole in the bush near Pine Creek 1984
Source: Unknown
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Darwin
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Alice Springs
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Adelaide
