The structure is described not as an ecclesia but a martyrion,⁸⁵ and specifically dedicated to St. John. This may not be significant, but it is worth speculating on these two facts. If the phylarch participated in the campaign against Khaybar, the presumption is that some federate soldiers died in the expedition and he may have erected the structure strictly as a martyrion to reflect his safe return and to remember those who died.⁸⁶
Source: wiktionary