This paper addresses the quantitative evaluation of ageing effects on liquefaction resistance of sand on the basis of experiences during recent earthquakes. Because of the practical needs of the people, emphasis is placed on the ageing in the recent 1000 years that have not been studied in details. Many uncertainties in case histories led to the idea of upper and lower bounds of ageing that successfully indicated the progress of ageing. The interest was extended to archaeological aspects and the site of an ancient man-made island, which had been missed for centuries, was identified. One of the very important causes of ageing is identified to be dislocation of sand grains and the minor cyclic shear during earthquakes promotes ageing. Therefore, seismically active countries enjoy increase of liquefaction resistance more rapidly than inactive countries.
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