In the libraries of Celsus at Ephesus and of Rogatianus at Timgad, the function of which is attested by inscriptions, bookcases are usually reconstructed in the niches. These examples have been used to identify other buildings which contained niches as libraries. However, Lora Johnson, in her 1984 Ph.D. thesis, rightfully questioned such an interpretation of the niches. The reconstruction of bookcases seems implausible, since the access to them would have been either impossible, or at least very difficult. The niches were more likely used for the display of statues. Similar arrangements can be found in various buildings, such as nymphaea or the scaenae frontes of theatres. Thus, the mere presence of niches inside a building does not allow to speculate about its function. This article aims at drawing attention to Lora Johnson’s work, the conclusions of which seem confirmed by new archaeological studies.