The story goes that between the defeat at Thermopylae and the arrival of the advance Persian troops at Athens, the Athenian leadership managed to remove the entire population of Attike to the island of Salamis. At this point it is commonly accepted that not all of the population went to Salamis, and that a sizable portion went either to Athens’ traditional rival Aigina,1to Salamis, or to the Peloponnese. For this reason, and simply the population of Attike at the time, the evacuation must have begun before Thermopylae. This may have also taken place under the supervision of Kimon, the son of Miltiades, since he was supposed to have led a procession among the first departures, Themistokles was with the fleet at Artemision, and the other two most prominent Athenian politicians of this section, Xanthippos and Aristides, were both Ostracized until almost immediately before Salamis.2
Now Xerxes sacked Athens, destroyed the acropolis, but after Salamis made preparations to withdraw, possibly disguising his intent by preparing to build a mole across to the island. In the fall of 480 Xerxes returned to Asia Minor, leaving Mardonios in Northern Greece with one large army, a second army in Thrace and a third in Northern Asia Minor. To set up these armies and withdraw at least beyond Thermopylae may have take upwards of two months past the Battle of Salamis, which took place in September of 480. Before the Battle of Plataia, Mardonios returned to Athens, first to enlist the Athenians to his side, and second to destroy the city as punishment when the refused. Purportedly he arrived in June of 479.
Assuming my time line laid out above from knowledge of the Persian logistical system, modern scholarship and superimposing the speeds on the way into Greece, this left at least six months between Xerxes’ departure and the return of Mardonios. Somehow between the two, at least some portion of Athenians decided that it was safe to rebuild and re-inhabit their city. Further, the process was well enough under way that it was worth the effort on Mardonios’ part to specifically come back, negotiate and then re-destroy the city, and possibly destroy a second harvest before withdrawing to Boiotia.
A second possibility is that the Persian army only destroyed the Acropolis the first time around. Strictly speaking Herodotus mentions that Thespiae and Plataia were sacked and that the temple complex on the Acropolis was destroyed when Xerxes took the city. That said it is hard to imagine that with such a huge force, and before and/or after losing Salamis, Xerxes did not simply have the city destroyed in its entirety. Further, he purportedly began construction of a mole to Salamis and, as Alexander would later do at Tyre, one convenient source of materials for a mole is a city (Alexander used New Tyre to build his).
While this thought process feels open ended, I have no answers, just a few half-completed thoughts about symbolism and that where the soul of a polis was the citizens, they needed that physical location, too. I just find the conception that rebuilding occurred so quickly after Salamis and before the Persian land army in Greece was defeated curious.
1 One of the reasons for the Athenian acceptance of Spartan hegemony is that it was a compromise Athens, Corinth and Aigina could accept and thereby both employ their fleets towards defense, rather than one or more withdrawing some or all to stop the others.
2 Unless the decree recalling the exiles took place before this time.