The Castle of Beersel is built on a narrow plateau on the edge of the flood plain of the river the Senne. A steep ridge borders the southern boundary of the plateau. Thanks to this strategic location, the castle controlled an important junction of waterways (Senne) and country roads (route Brussels - Halle - Mons). The location explains why the castle is more sturdy in structure on the northern and western side than on the southern and eastern side. The three massive corner towers of the castle are indeed clearly oriented towards the Senne Valley. In addition, the castle was built on the bank of a swampy micro-valley carved by a tributary of the Senne. The moat surrounding the castle was permanently supplied with water from several watercourses which find their source in the ridge. The sudden drop in water level caused heavy erosion in the upper course. As a result, large volumes of sediments were deposited in the moat. A few trial trenches in the bottom profiles revealed the presence of several cuts. These cuts may be due to local re-excavations of the moat, after it had been completely silted up due to sedimentation of the eroded material. Another possibility is that the moat area against the foundations of the castle was dug out deeper in certain places to prevent the moat from running completely dry if the only water supply was cut off in times of conflict.
