Augustinian monks established a monastery on Eskilsø at the beginning of the twelfth century.

The ruins of the little church, built of granite boulders and travertine, are still to be seen on the highest point of the island, but otherwise there is not much of the monastery left. Færgegården museum in Frederiksund has recently excavated the area around the church. Remnants of the monastery’s other buidings have been found, but most of it has been ploughed away in the course of time. It is however thought that many of the plants on Eskilsø were introduced by the monks, for example Mullein, Houndstongue, Black Horehound and Greater Burdock.

The monastic community did not stay on Eskilsø for very long, as Abbot Vilhelm moved it to Æbelholt near Hillerød in 1175.

There have been a lot of stories (all stemming from a single source) to the effect that the monastery was closed down because of the monks’ wicked ways with the women of Roskilde etc, but it is doubtful whether these stories have any basis in fact.