Short answers, pulled from the story.
The trading port of Birka emerged in the year 750. This settlement became one of the earliest urban centers in Scandinavia and served as a Baltic link connecting Ladoga and Novgorod to the Byzantine Empire.
Rimbert wrote Vita Ansgari around 865 to describe missionary work at Birka starting in 829. The text details how King Björn met Ansgar when he arrived in 829 and mentions that Herigar built a church on his ancestral property near where tings were held.
Entomologist Hjalmar Stolpe conducted archaeological excavations on Björkö between 1871 and 1895 after discovering large amounts of amber. These digs revealed approximately seven hundred people lived at Birka when it reached its largest size and uncovered about three thousand graves.
The silver alloy ring found between 1872 and 1895 became known as the Allah ring because Annika Larsson claimed in 2017 that a textile bore Arabic words Allah and Ali. Marijn van Putten argued the inscription represented pseudo-Kufic with no meaning in Arabic while other analysts believed the engraving linked Vikings directly to Islamic civilization.
Birka ceased operations around 975 AD coinciding with Sigtuna's founding as a Christian town thirty-five kilometers northeast. Coins dating suggest the city died out approximately 960 and reasons for decline remain disputed among historians including speculation by Neil Kent regarding enemy assault.