The name Diegem
The name appears in the sources in many forms: Dydenghem (1223), Diedenghem (1253), Diedeghem (1259), Didenghem (1269), Dyedegem (1390–1424), Dyeghem (1479), Dieghem (1587), Digum (1652), Diegom (1690–1691), Diegum (1700) and Dighem (1759). The present spelling, Diegem, has only been used since 1937.
What the name means is uncertain. For a long time it was thought to be the home of a Frank with a name like Dido, Theodo or Thiuda. Another explanation sees in 'did' an old Indo-European word for marsh, as in the place name Didisheim. Diegem would then be 'the settlement by the marsh', which fits the wet Woluwe valley, with names such as Diegembroek, Broekstraat and Broekmolen.
Earliest traces
Around 1810 some forty coins bearing the image of Louis the Pious were found. In 1948 Karel De Kempeneer came across a Gallo-Roman grave in his sandpit; J. Mertens’ excavations in May 1950 revealed a cremation cemetery from the late 2nd and early 3rd century. In 1972, during the demolition of the De Coninck cardboard factory, workers found the grave of a Frankish warrior with his horse; it was never studied scientifically.
The first settlements
The oldest settlement lay around the Voorde, the crossing over the Woluwe, and later near the castle and church. On either side of the Voorde lay two estates: Cuddegem, the later De Reine castle, and Diedegem, with the stronghold of the lords of Diegem. To the south lay Nijpezele, which later grew into Diegem-Lo. Cuddegem, Nijpezele and the Hof ten Bossche belonged to the lordship of Wezembeek.
Administratively Diegem belonged to the mayoralty of Vilvoorde in the duchy of Brabant. As a parish it came under the diocese of Cambrai until 1559 and then under the archdiocese of Mechelen; from 1873 it belonged to the deanery of Zaventem.
Kornelimünster and Saint Cornelius
Diegem probably came into the hands of the abbey of Kornelimünster near Aachen as early as the 9th century, through a gift from the emperor. No deed survives, but the cult of Saint Cornelius – the abbey’s patron – strongly points that way. A first church is mentioned in 1379. Between 1273 and 1280 the impoverished abbey sold its revenues around Brussels but kept the tithes, which passed to the abbey of Heylissem in 1749.
The lords of Diegem
In 1265 Giselbert van Didenghem is mentioned, a vassal of the lord of Perk. Around 1384 Margareta van Diedeghem brought the seigneury to Jan van Brecht, of a Brussels patrician family. Karel van Brecht (1518–1595), mayor of Brussels in 1559 and 1561, bought high, middle and low justice over Diegem in 1558. Through his daughter Gertrudis, Diegem passed to the Oudart family; Catharina Oudart (d. 1629) married Filips Happart.
Jan Antoon Happart sold the seigneury in 1756–1757 to Pieter Albert Piermans, who was made a baron in 1757; on 28 April 1763 Diegem was raised to a barony. It then passed to, among others, the de Lanfranchy and Le Boucq de Beaudignies families. In 1902 August Ulric Marga bought the castle.
Seal and arms
On 13 September 1507 Diegem received its own aldermen’s seal. It showed a lion; in 1902 Saint Cornelius was added, holding the shield. This became the coat of arms Diegem used until the merger.