Municipal Sewer Vent, Sydney

As Sydney developed, its watercourses became open sewers, and the resulting pollution forced construction of Sydney's first sewerage system.

The system was planned by City Engineer Edward Bell and consisted of five principal outfall sewers discharging to the harbour at Blackwattle Bay, Darling Harbour, Sydney Cove, Bennelong Point and Woolloomooloo; the system was completed in 1857.

At the highest point of the system – the corner of today’s Elizabeth and Bathurst Streets on the edge of Hyde Park, a vent shaft was built to eliminate noxious gases from the sewer. It was of brick and sandstone and disguised as an Egyptian style obelisk. The obelisk was the first and only major sewer vent and is now one of the oldest extant items of infrastructure connected with Sydney city's first sewerage system.

The obelisk itself has remained largely intact, however there have been various maintenance works including the replacement of the copper vent and changes to the configuration of the obelisk's surrounds.

Within a few years of construction of the sewerage system there was an uproar at the pollution it caused of the Harbour, forcing restructuring of the system, with some of the original sewers being converted to stormwater drainage. Sydney’s sewers were later diverted to cliff-face outfalls at North Head, Bondi and Malabar, but the pollution they caused of the ocean and beaches, eventually forced construction of deep water ocean outfalls at those places; these commenced operating in 1990-91.