The meaning and significance of Australia Day has evolved and been contested over time, and not all states have celebrated the same date as their date of historical significance. Unofficially, or historically, the date has also been variously named "Anniversary Day", "Foundation Day" and "ANA Day". It has also been known as "Invasion Day" and "National Day of Mourning". The date of 26 January 1788 marked the proclamation of British sovereignty over the eastern seaboard of Australia (then known as New Holland). Although it was not known as Australia Day until over a century later, records of celebrations on 26 January date back to 1808, with the first official celebration of the formation of New South Wales held in 1818. On New Year's Day 1901, the British colonies of Australia formed a federation, marking the birth of modern Australia. A national day of unity and celebration was looked for. It was not until 1935 that all Australian states and territories adopted use of the term "Australia Day" to mark the date, and not until 1994 that the date was consistently marked by a public holiday on that day by all states and territories.