South Australian state border origin partly due to Spain-Portugal treaty that divided up the world in 1494
Maps showing the history of South Australia's boundary anomalies.
Maps courtesy Dr Gerard Carney
South Australia’s state borders, abutting every other mainland state, are an historical oddity that retain their quirks.
The South Australian Colonisation Act 1834 defined the boundaries on the west at 132 degrees longitude and on the east at 141 degrees longitude. The official reason for choosing the 132 degrees western boundary is obscure but it may be linked to it running through Eyre Peninsula’s Fowler’s Bay, mentioned by Matthew Flinders as bring the first protected bay after the inaccessible Great Australian Bight cliffs.
But the 132 degree western border left South Australia surrounded by New South Wales as it was in 1836. The New South Wales western border, at 129 degrees, was shared with the new Western Australia from 1831. This left a No Man’s Land on South Australia’s west between its border and the WA/NSW border. This anomaly was only eliminated in 1861.
The reason for the original New South Wales border being at the 129 degrees longitude is rooted in history going back to the 1494 Treaty of Tosdesillas (followed by the Treaty of Zaragoza 1529), dividing control over the New World (including the then-unknown Australia) between Spain and Portugal. The Briish roughly respected this divide when colonising Australia to avoid unsetting anyone.
The unmarked eastern border between New South Wales and South Australia became a pressing concern. Eventually, after exploring alternative border possibilities, the two colonies agreed to have their surveyors, Wade and White, mark out a Glenelg River section of boundary line that was officially proclaimed by 1849.
A Wade-White Line was continued to the River Murray in 1850 and it became the South Australia border with Victoria that came into that year. But more accurate technology in 1868 revealed that the Wade-White Line was two miles and 19 chains west of the 141 meridian. South Australia tried unsuccessful appeals all the way to the Privy Council in Britain to have the boundary moved eastward and the issue remains unresolved with the border between the two states running down the middle of River Murray for 11km.
South Australia’s other major border change was its takeover of the Northern Territory from New South Wales in 1863. It later regretted the move and willingly surrendered the territory to the federal government in 1907.