Analysis of charcoal fragments derived from different layers within each cesspit shows that beech (Fagus sylvatica), alder (Alnus sp.) and oak (Quercus sp.) were most commonly used as firewood. Birch (Betula sp.) is also frequently represented but hornbeam (Carpinus betulus), alder buckthorn (Frangula alnus), poplar (Populus sp.) and willow (Salix sp.) only rarely ended up on a fire inside the tower (table 3). This pattern is not surprising: oak and beech are ideal for burning, both as firewood and as charcoal. Alder is less suited for firewood but produces good quality charcoal (Gale & Cutler 2000). From the fragments investigated, it could not be seen whether wood or charcoal was used predominantly. The results from the pollen analysis and the study of macrobotanical remains suggest that peat was also used as fuel. Remarkably, the charcoal spectrum seems to differ between both cesspits, with structure 2 containing more beech and oak, but structure 4 significantly more alder. The patterns observed, however, may be the result of random events.