It was declared a National Monument under old NMC legislation on 10 December 1965. The British Army approached Pretoria at Wierda Bridge (Six Mile Spruit) on 4 June 1900, the Royal Artillery and the Royal Garrison Artillery retreated from the Burghers through Pretoria over this Bridge, during the Anglo-Boer War.

Also known as the Sesmylspruit Bridge, close to the Old Johannesburg Road intersection with Wierda Road, this steel girder Bridge is one the first of its kind to be Built in South Africa. It was Built in 1891 and is based on the hinge system, with heavy hinge-and-nut-bolts connecting the main parts at the knot points. The Technical Design and Construction was done with great care and skill, with the footings being lower than the water line. The Bridge was Designed in the offices of the Department of Public Works, ordered from Germany, delivered to Natal and then transported by ox wagon to the Site.  This Bridge was completed in 1891 by Sytze Wierda. Director of Public Works of the South African Republic
 
Architect: 
Sytze Wopkes Wierda
Sytze Wierda was Born in the Netherlands and was renowned as the first Government Architect and Engineer for the Zuid-Afrikaansche Republiek (ZAR). Over the fourteen Years of working for the Government, he and his team developed the Republican Style (also known as Eclectic Wilhelmiens), Designing numerous significant buildings. His exact Town of Birth is disputed and even his Architectural Education is unclear, though it is known that he was originally Schooled to be a Carpenter. The Suburb Wierdapark, in Centurion, is named after him.
 
Geolocation
-25° 42' 3.5172", 28° 11' 15.5652"
References

9/2/258/0162.
http://samilitaryhistory.org/vol131dp.html
artefacts.co.za/architect (accessed 20 January 2014).
http://www.dutchfootsteps.co.za

Further Reading
https://www.sahistory.org.za/franco/historical-conservation-nationalist.html