The last remnant of the West Roman Empire was conquered in 486 when Clovis defeated Syagrius who had ruled over northern Gaul. That part of the Frankish kingdom would be called Neustria (the New Land) as opposed to Austrasia (the Eastern Land), which was the original core territory of the Franks.
Grab bar mounting brackets made specifically for fiberglass installation have discs that safely distribute the weight of a person and prevent the fiberglass from cracking. By attaching the brackets to wall studs with bolts, you ensure that the grab bar will not pull out from the tub or shower wall when in use.
Ideally you would want to install the grab bars onto wood studs, whether there is tile or not. However, most grab bars are not sized to precisely span the standard 16 center-to-center spacing of wall studs. Some installers will purchase longer bars... 18 or 24... and install them at an angle so that each end aligns with a stud. However, all homeowners do not want this askew installation.