Chemical and electron optical examinations of waterlogged archeological oak woods from5000 years show various grades of changes of their ultrastructure compared to fresh oak wood. The changes are independent of the age of the samples. They range from swelling of the cell walls, to progressive stages of dissolution of carbohydrates from the central cell wall layers, to ultimate absence of structure supporting carbohydrates resulting in the collapse of the residual lignin skeleton of the cell walls. The degree of degradation of the ultrastructure cannot always be derived from the outer appearance of the wood. Only with drying, does irreversible collapse of the residual structure occur in heavily degraded wood, which leads to an extraordinary shrinkage of the sample. -- AATA