.This Beacon marks, the Northern Boundary of the Farm “Randjeslaagte" on which Johannesburg was laid out in 1886. 

The Randjeslaagte Beacon stands in Boundary Road, Parktown, just off Louis Botha Avenue, one of the busiest Traffic Arteries of Johannesburg. Boundary Road enters Louis Botha Avenue at its Highest point. The Beacon is a simple concrete Structure standing on a Natural Rock Outcrop.
When the farms; 'Turifontein, Doornfontein, Braamfontein and Langlaagte', were originally given out, a Triangular piece of land was not included in any of them; it remained Crown Land and became known as Randjeslaagte. The Beacon marked the Northern corner or apex of the Farm. The Western Boundary is marked by Diagonal Street and the South Western Corner by the Junction of Diagonal and Commissioner Streets; the Eastern Boundary is today marked by End Street.
For years the Owners of the Adjoining Farms, who regarded this piece of unappropriated Land as of no value, Grazed their Cattle on it, when grazing was scarce. But the discovery of Gold in the beginning of 1886, brought this despised little piece of Land into the very heart of the famous City of Gold.
On 3rd August of that Year the Government of the Zuid-Afrikaansche Republiek instructed a Commission, to select a suitable Site for a Town, on the newly-discovered Witwatersrand Goldfield. The Commission consisted of; 'Christiaan Johannes Joubert, later head of the Department of Mines, and Johann Friedrich Bernhard Rissik, the Surveyor-General'. Their choice fell on Randjeslaagte. Johann Rissik drew up a General Plan of the new Township and the tender of Jos. E. de Villiers to Survey the erven was accepted. On 4th October, 1886, Randjeslaagte was proclaimed a public diggings and on the following day Rissik wrote to D Villiers that ‘the government has thought fit to accept your tender for surveying 600 erven on the government land Randjeslaagte. The town to be laid out by you will bear the name of Johannesburg’. In this way Randjeslaagte Farm became Johannesburg, called after Johann Rissik and Christiaan Johannes Joubert.
In the course of time the grass and bush of Randjeslaagte Farm, gave place to the concrete and macadam of the heart of Johannesburg which had meanwhile expanded far beyond the Boundaries of the original Triangle. But the old Beacon has by some good fortune been preserved and now bears witness to the humble Origin of the proud City of Johannesburg, proclaimed in 1965.
-26° 10' 51.6", 28° 2' 56.4"
Further Reading
https://www.sahistory.org.za/.../historical-conservation-historical-datesJHB. html