Erguel Castle is a ruined castle in the municipality of Sonvilier in the canton of Bern in Switzerland. It is the best preserved castle ruin in the French-speaking Bernese Jura.HistoryDuring the 11th century, the Lords of Erguel, or Arguel, moved from Franche-Comté and settled in the village of Sonvilier. Exactly when they built Erguel Castle on a hill south-east of the village is unknown, but in 1178 and 1184 Heinrich von Erguël was mentioned ruling over the region. The knights of Erguel owned land in the surrounding valley and held the vogt office over the church at Saint-Imier. The family kept the castle, the surrounding land and the lordship until 1264 when Otto von Erguel, who at the time lived in Basel, ceded them to the Prince-Bishop of Basel. In return the bishop granted him lands in Alsace.The bishop appointed a bailiff for the castle, but administered the extended lands out of Biel. The castle was the southernmost point in the episcopal dominion. Under Bishop Heinrich of Isny (1275-1286) the castle was strengthened and expanded. The currently visible parts of the castle probably all date to this construction period. It can be assumed that the visible parts of the plant today to go back to that time.