Fort Pentagouët (Fort Pentagoet, Fort Castine, Fort Penobscot, Fort Saint-Pierre) was a French fort established in present-day Castine, Maine, which was the capital of Acadia (1670–1674). It is the oldest permanent settlement in New England.
Its commanding position at the mouth of the Penobscot River estuary, a lucrative source of furs and timber, as well as a major transportation route into the interior, made the peninsula of particular interest to European powers in the 17th century. Majabagaduce (as the Indian name would be corrupted) changed hands numerous times with shifting imperial politics. At one time or another, it was occupied by the French, Dutch and England's Plymouth Colony.
Castine was founded in the winter of 1613, when Claude de Saint-Étienne de la Tour established a small trading post to conduct business with the Tarrantine Indians (now called the Penobscots).
After the trading post was established at Castine, a raid by English captain Samuel Argall at Mount Desert Island in 1613 signaled the start of a long-running dispute over the boundary between French Acadia to the north and the English colonies to the south. There is evidence that La Tour immediately challenged the English action by re-establishing his trading post in the wake of Argall's raid.Captain John Smith charted the area in 1614 and referred to French traders in the vicinity. In 1625, Charles de Saint-Étienne de la Tour erected a fort named Fort Pentagouët.
English colonists from the Plymouth Colony seized it in 1629, and made it an administrative outpost of their colony. Colonial Governor William Bradford personally traveled there to claim it.