Basilica B is the most impressive single structure at Philippi — a vast 6th-century domed church that was never completed because the dome and arches collapsed during construction. The five tall brick piers still stand, the marble pavement is still in place, and the pieces of fallen vaulting lie around them. Walking around the basilica gives you a vivid sense of an ambitious building that did not quite work.
The basilica sits on the south side of the Via Egnatia, immediately south of the forum. Combine it with the forum visit; the two are functionally one stop.