Thietmar names "Siegfried and his son" among those who plotted against Heinrich II “der Zänker” Duke of Bavaria in his rebellion in 984.
Graf von Northeim 1002. Thietmar names "Ethelind" as wife of Count Siegfried, recording that she welcomed Ekkehard I Markgraf von Meissen at Northeim in 1002 and warned him that her husband's sons "Sigifrith and Benno" were plotting to kill him.
Married firstly Mathilde, daughter of ---. The Annalista Saxo names "comitissa Machtilde" as wife of "Sigefridus comes de Northeim".
Married secondly Ethelinde, daughter of ---. Thietmar names "Ethelind" as wife of Count Siegfried, recording that she welcomed Ekkehard I Markgraf von Meissen at Northeim in 1002.... The text implies that Ethelinde may not have been the mother of the sons in question. However, the fact that Siegfried's great-granddaughter was named Ethelinde suggests a blood relationship with Ethelinde senior. Another possibility is that "comitissa Machtilde" and "Ethelind" were in fact the same person, mother of both Siegfried's sons. 1
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