Battle of Svolder, Viking Age.

1000 (M) was a leap year starting on Monday of the Julian calendar, the 1000th year of the Common Era (CE) and Anno Domini (AD) designations, the 1000th and last year of the 1st millennium, the 100th and last year of the 10th century, and the 1st year of the 1000s decade. As of the start of 1000, the Gregorian calendar was 5 days ahead of the Julian calendar, which was the dominant calendar of the time.

The Battle of Svolder was a large naval battle during the Viking age, fought in September 1000 in the western Baltic Sea between King Olaf of Norway and an alliance of the Kings of Denmark and Sweden and Olaf's enemies in Norway. The backdrop of the battle was the unification of Norway into a single independent state after longstanding Danish efforts to control the country, combined with the spread of Christianity in Scandinavia.

The Viking Age was the period during the Middle Ages when Norsemen known as Vikings undertook large-scale raiding, colonising, conquest, and trading throughout Europe and reached North America. The Viking Age applies not only to their homeland of Scandinavia but also to any place significantly settled by Scandinavians during the period. Although few of the Scandinavians of the Viking Age were Vikings in the sense of being engaged in piracy, they are often referred to as Vikings as well as Norsemen.

September 9 is the 252nd day of the year in the Gregorian calendar; 113 days remain until the end of the year.