A slewing bearing having two rings and rollers arranged between the rings, wherein one of the rings is provided with a through-hole for inserting the rollers for assembly and maintenance, and with a plug for closing the through-hole. The through-hole is formed as a bore including an inner portion with a smaller bore diameter and an outer portion with a larger bore diameter. The smaller diameter portion is reduced in order to facilitate the assembly, while avoiding an increased diameter in the innermost part of the thorough hole in order to secure stability and robustness.