Short answers, pulled from the story.
Grobiņa is a town and the administrative centre of South Kurzeme Municipality in the Courland region of Latvia, eleven kilometers east of Liepāja. It was founded by the Teutonic Knights in the 13th century and received its town charter in 1695.
During the Early Middle Ages, Grobiņa was the most important political centre on the territory of Latvia. It hosted a Scandinavian settlement on the Baltic Sea comparable to Hedeby and Birka, and the roughly three thousand surviving burial mounds there represent the most impressive Vendel Age remains in Northern Europe.
Birger Nerman excavated the settlement in 1929 and 1930. He found an earthwork stronghold protected on three sides by the Ālande River, along with three Vendel Age cemeteries dateable to 650-800 AD. The burial evidence indicated a colony of Gotlanders living under the protection of a Swedish military garrison.
A picture-stone found in a Grobiņa grave in 1987 depicts two duck-like birds with beaks meeting inside a ring of ornaments, stylistically dated to the second half of the 7th century. Such picture-stones, known as bildsten, are otherwise unique to Gotland, where several hundreds have been found, making this a rare artifact carried to Latvia by Gotlandic colonists.
According to Rimbert's Vita Ansgari, Olof I of Sweden destroyed the settlement, known as Seeburg and generally identified as Grobiņa, during a campaign around 854 AD. Seeburg had seven thousand armed men, but the town was pillaged, ravaged, and burnt by the invading Swedish army after local Courlanders had rebelled against Swedish tribute demands.
Birger Nerman's excavations at the ancient fort of Apulia (modern Apuolė in Lithuania) found large concentrations of Swedish arrowheads near the walls of the ruined Curonian fortress. This physical evidence corroborated Rimbert's account of a large-scale 9th-century conflict in the region.