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Ermengarde of Hesbaye, or Irmengarde (c. 778 – 3 October 818) was Queen of the Franks and Holy Roman Empress as the wife of Emperor Louis I. She was Frankish, the daughter of Ingram, count of Hesbaye, and Hedwig of Bavaria. Her family is known as the Robertians.

In 794/5 Ermengarde married Louis the Pious, king of Aquitania, king of Franks, king of Italy, ruler of the Holy Roman Empire.

She had six children:

• Lothair I, born 795 in Altdorf, Bavaria
• Pepin I of Aquitaine, born 797
• Adelaide, born ca. 799
  • Possible wife of Robert the Strong, possible mother of Odo, Count of Paris and Robert I of France.
• Rotrude, born 800
• Hildegard / Matilda, born ca. 802
  • Wife of Gerard, Count of Auvergne, possible mother of Ranulf I of Poitiers.
• Louis the German, born ca. 805

She died at Angers, France on 3 October 818. A few years after her death, her husband remarried to Judith of Bavaria, who bore him Charles the Bald.