Which Viking-era Norwegian town was known in Old Norse as Niðaróss?

Trondheim was known in Old Norse as Niðaróss during the Viking Age and medieval period.

The settlement was founded by King Olaf Tryggvason in 997, according to the traditional account. It stood at the mouth of the River Nið, whose name appears in the Old Norse form Niðaróss, meaning the estuary or mouth of the Nið.

Trondheim became an important political and religious centre. After the death of Olaf Haraldsson, later known as Saint Olaf, his shrine at Nidaros attracted pilgrims. Nidaros Cathedral was eventually built over the traditional site of his burial.

The name Nidaros was replaced in common use by Trondheim, a form connected with the surrounding district of Þróndheimr. Modern Trondheim is therefore the same city that medieval sources call Niðaróss. It is distinct from Bergen, which became a major Norwegian royal and trading centre later.