Due to economic reasons, natural stones (armourstones) of various sizes and qualities are very frequently used for the constructions of the breakwaters to protect coastal engineering structures from wave actions. Deterioration of the armourstones with time in the form of abrasion and disintegration may end up with the damage of the structures. Therefore, it is necessary to investigate the long-term performance and quality of the armourstones, which should be sound and durable. Mersin and Kumkuyu harbours were constructed using four different limestones obtained from two quarries. The limestones have different characters and site performances. In this study, the material and mass properties of the limestones taken from the quarries with known site performances as armourstones are investigated. The site performances and durability of the limestones are compared with the field measurements and laboratory works. Thus, the information obtained is used to assess long-term durability of the armourstones. The long-term performance of the Degirmencayi and Tirtar upper level limestones are observed to be good whereas it is rather poor for the Tirtar middle and lower level limestones. Comparison between the predicted and observed durabilities of the armourstones indicated that CIRIA/CUR, RDI(d), RERS, and wet to dry strength ratio give better results based on their field performances. However, the prediction of the durability of the limestones is poor in case RDIs, average pore diameter, and saturation coefficient are used.