Pella is a site that lies close to my heart. I have spent much time here, both physically and scholarly.

But I do have one question: which source specifically outlines Pella as capital? This is generally assumed to happen under Archelaos, and probably at the end of his rule. But, no explicit mention is made of the city! In fact, it seems that our identification of the city as "capital" comes from Xenophon's later description of Pella as the "largest" Macedonian city in Cleigenes' appeal to Sparta for assistance against Olynthos:

5.2 [12] Thereupon Cleigenes of Acanthus spoke as follows: “Men of Lacedaemon and of the allied states, we think you are unaware that a great danger is springing up in Greece. To be sure, almost all of you know that Olynthus is the largest of the cities on the coast of Thrace. These Olynthians, in the first place, attached to themselves some of the cities with the provision that all should live under the same laws and be fellow-citizens, and then they took over some of the larger cities also. After this they undertook, further, to free the cities of Macedonia from Amyntas, king of the Macedonians. [13] And when the nearest of them gave their allegiance, they speedily proceeded against those which were farther away and larger; and we left them already in possession of a great number of Macedonian cities, including especially Pella, which is the largest of the cities in Macedonia. We also had information that Amyntas was withdrawing from his cities and had already been all but driven out of all Macedonia..."

Pella is not even described as the seat of the king! Any thoughts?