A method for quick-opening a set of rolls in a calender, in particular a supercalender, in which a paper or board web to be calendered is passed through calendering nips formed by a variable-crown top roll, a variable-crown bottom roll and by two or more intermediate rolls arranged between the top and bottom rolls. The rolls are arranged to form a substantially vertical stack of rolls, and the intermediate rolls are supported by the use of hydraulic relief cylinders so as to relieve the nip load produced by the mass of the bearing housings of the intermediate rolls and auxiliary devices associated therewith. During the quick-opening of the set of rolls, the bottom roll of the set of rolls is lowered and the relief pressures in the hydraulic relief cylinders are discharged so as to open the calendering nips. The hydraulic oil flowing out from the relief cylinders is controlled by valves connected to the relief cylinders of each intermediate roll so that, during quick-opening of the set of rolls, the roll nips may be opened in a controlled manner in a desired order. A hydraulic system for the set of rolls is also disclosed.