The abbey of Kornelimünster lies on the Inde, near Aachen. Emperor Louis the Pious founded it at the end of 814 or early 815 for his confidant Benedict of Aniane, who wanted to reform the Benedictine rule there; it was consecrated around 817. It received vast estates throughout the empire and a rich treasury of relics, including relics of Saint Cornelius given by Charles the Bald. It is named after him. Cornelius was pope from 251 to 253, at a time of persecution of Christians, and died in exile.
Diegem probably came to the abbey as early as the 9th century; no deed survives. The estate of Diegem and that of Neder-Heembeek on the Senne formed a single whole, linked by the Ham, a landing place on the Senne. Of all its estates, the abbey introduced the cult of its own patron only in Diegem and in Sint-Kornelis-Horebeke near Ronse.
An abbey short of money
The 13th century was a disaster for the abbey. Impoverished by wars, it sold its revenues around Brussels between 1273 and 1280; those of Diegem went for 801 pounds to Godfried, a cleric. Yet Kornelimünster remained the landlord: it sold revenues, not the village itself. What remained were chiefly the tithes, the Duivenmolen and a few plots of land. By 1418 the abbey itself no longer knew exactly what still belonged to it, and the Duke of Brabant had the local officers track down the fiefs that had been ‘obscured’.
Around the Duivenmolen at Nijpezele the patron's name was everywhere: the St Cornelius lime tree (1614, 1748), a St Cornelius chapel (1748), the Sint-Cornelis brook (1632) and the St Cornelius road. In 1727 the abbey still owned in Diegem half a bunder of meadow, the Duivenmolen, a small orchard, four little ponds and an annuity on the mill.
Heylissem takes over
In 1749 the tithes of Kornelimünster passed to the abbey of Heylissem, a Premonstratensian abbey on the Kleine Gete founded around 1129-1130. Like Kornelimünster before it, it paid the parish priest of Diegem a share of the tithes. The abbey was completely rebuilt around 1780 by Laurent Dewez and sold by the French Republic in 1797; later it housed a cotton mill and a sugar factory. In 1962 the province of Brabant bought the estate.
Other religious houses with property in Diegem
Other institutions also owned land in Diegem. The convent of Bethany in Mechelen had the Hof van Bethaniën there. The infirmary of the Great Beguinage of Brussels owned more than 33 bunders in 1744; the Begijnenweg still recalls it. The St John's Hospital of Brussels had a map of its Diegem property drawn in the early 18th century. The Minor Canons of St Gudula had their own estate there with its own mayor from 1226, and the abbey of Grimbergen and the lepers of Obbrussel are also mentioned.