The territorial behaviour of A. imperator was studied using a marking technique at a small pond in central Italy. The 66 hold the whole pond or a definite part of it, patrolling above the water and fighting against other 66, until they are displaced or leave spontaneously. The time spent by a 6 on his territory ranges between less than 1 min. and 93 min. and shows a general trend to decrease in successive days with decreasing crowding. 66 may change territory inside the pond, but some of them exhibit a preference for some part of the pond. This form of spacing pattern is compared with other ones which have recently been described in other species of dragonfly.