In making the announcement Melissa Price stated that ‘Centennial Park was selected for its “outstanding heritage value to the nation” as the site chosen for the inauguration of the new Australian nation’. 
Centennial Park was the site of the official ceremony held on 1 January 1901 to mark the federation of the six colonies and the proclamation of the Federal Constitution. The ceremony was preceded by the “Great Inaugural Procession”, which travelled from the Domain to Centennial Park. Over 250,000 people lined the streets to watch the Procession.
On reaching the Park Lord Hopetoun and Edmund Barton were sworn in respectively as Australia’s first governor-general and first Prime Minister respectively. The first Cabinet was sworn in at the same time. There were over 60,000 onlookers assembled on Federation Valley to witness this historic event in the specially constructed outdoor pavilion.
Why should oaths have been administered and the proclamation read within the close shut walls of any building when Nature has endowed the people with this fine park commemorating the foundation of Australia? 
2018 also marks the 130th anniversary of the opening of Centennial Park, which NSW Premier Sir Henry Parkes declared the “People’s Park” on 26 January 1888.
RAHS President Christine Yeats spoke to 2GB’s Michael McLaren about the history of the park, including its early history as a swampy wasteland to its significance with Australian Federation. Those who are interested can listen to the interview online.
References: ‘Sydney’s Centennial Park heritage listed, Sydney Morning Herald, 2 October 2018.
 From the First Governor-General Lord Hopetoun’s Inauguration of the Commonwealth of Australia speech, 1 January 1901, Centennial Park. Centennial Park, Australian Government: Department of the Environment and Energy, <http://www.environment.gov.au/heritage/places/national/centennial-park>, accessed 3 October 2018.