So first it’s worth noting that there actually is a modern city called Sparta by the site of the ancient ruins, so it’s not entirely true it’s not still around. However, it is true that there is less continuity between the modern Sparta and the ancient Sparta, and (greater) Athens is a huge metropolis and national capital of 3 million while Sparta has a population of 35,000 - a bit like comparing the once similarly sized London and Colchester in current England. So what happened?

The issue isn’t about the Pelopennesian War. This was an important war and of particular note due to the vivid and detailed account given by Thucydides, jokingly referred to as the first ‘realistic’ historian (Herodotus having been less so). Famously, at the end of the war, Sparta is described as having spared Athens where the leaders of Corinth and Thebes wanted Athens destroyed. If this is true (such destructions were not unheard of) and it had happened, we may not have this question at all.

But the war wasn’t unique, at all. The Greek city states continues to find a bewilderingly complex series of wars among each other for most of the next century, with Spartan hegemony going back and forth, giving way to Theban, with Athens’, Sparta’s, Corinth’s and Thebes’ fortunes waxing and waning in shifting alliances, eventually seeing the brief rise of Thessaly… until Macedon burst on the scene and essentially swept up almost the whole of Greece (and much beyond). From then on, and with the shift of learning and power to other Hellenistic centres like Alexandria, the major old Greek city states all went into decline.

Sparta continued to be quasi-independent for a long time, first fending off Macedonian power and fighting its Achaean neighbours until siding with Macedonia against Rome. Eventually Rome gave the Spartans a qualified autonomous status, respecting them for their legendary status as warriors, and the was even growing again by the fourth century. Athens, however, was supported by the Romans as more of a hub of culture and learning. Athens’ status as the early hub of Greek (and thus Western) literature, language, philosophy and learning would consistently afford it special status that Sparta lacked, with very real consequences even to the present day.

The big difference though is 800 years after the Pellopennesian War: in the late 4th century both cities were still sizeable, but then the Goths under Alaric swept in Greece and sacked them both. The next century, the Slavic and Avar invasions of Greece led to a massive influx of Slavs into most of the Peloponnese and in fact most of western Greece, except those cities on the east coast Constantinople could more easily reach and protect. So if I had to point to one factor, it would be this: Athens was on the eastern coast and closer to Constantinople, as well as in a desirable port location, so that Constans II and other emperors could set up garrisons there and rebuild what the Goths and Slavs had damaged. Sparta, further off to the south-west, had no such luck, and was virtually emptied. It is in fact a matter of debate whether it was entirely emptied for a while, or whether a small population remained - and whether they were chiefly Greeks or Slavs, and whether the region was later replenished with Greeks, Slavs were Hellenised, or whether the population had ever been mostly expelled. What is true is that Sparta was reduced at most to the population of a small village, and its major buildings reduced to ruins.

Athens’ status as the centre of learning led to its Attic dialect dominating from the late Classical Greek period onwards. Today, all dialects of Greek mainly descend from it - with the sole exception of Tsakonian, a small, endangered dialect (or language, depending on whom you ask) descended from the dialect of Sparta. This difference in status would continue to be relevant.

During the 13th century, after the Fourth Crusade, Western crusaders, as well as Venetians, Genoese, Normans and others swept into the old Byzantine empire and took Constantinople itself and split Greece between them into a complex array of shifting states, called the ‘Frankokratia’ or ‘Frankocracy’ in Greece and ‘Latin Empire’ in Constantinople - ‘Latin’ and ‘Frank’ being what the Greeks generally called Western Europeans. Athens was held as a duchy of its own, with its name adding status to its succession of Burgundian, Sicilian, and Florentine rulers. Much of the Peloponnese on the other hand was ruled by a Norman family for some time, including the very military-minded and expansionist William II Villehardouin, who built his capital, a major fort, at Mystras, just a few miles from Sparta. This may have shifted any remaining focus away from Sparta and reduced it further, though again it is unclear what the population actually was over this period. The Byzantines reconquered the region but William II’s fort at Mystras was impressive enough to remain the regional capital.

The other major factor comes only in the last two hundred years, when Greece fought for its independence. Greek culture had been largely focused on Christianity and the Byzantine tradition for well over a millennium (under Byzantines, ‘Latin’ states and the Ottoman Turks) - even down to people’s names. But a new wave of Romantic nationalism swept Greece during their 1822-1832 war of independence against the Ottomans, partly encouraged by Western European scholars and adventurers who came to help fight for the country they had spent so much of their education learning about. A new awareness of and pride in the status of classical Greece worldwide led to a boom in learning and nationalism around their ancient forebears, and although Athens was a moderately sized city, it was for this reason above all the obvious choice for the capital of the new state, which boomed again, reaching its current size.

By the same token, however, there was some Romantic cultural memory of the greatness of Sparta too, and in 1834, the Greek king Otto I decreed that Sparta should be expanded into a full city again. It still only has a bit more than 1% of the population of Athens (a stark difference from the classical period), and its continuity is debatable, but that is where things now stand.

In summary, then, I’d argue the chief reasons are: Athens could more easily be retaken and defended by Constantinople after the Gothic and Slavic invasions, while Sparta was further away and inland; any village-sized habitation of Sparta was overshadowed by the nearby fortress of Mystras in the Middle Ages; and the status of Athens as the seat of ancient Western thought led to enthusiasm to expand it and make it the capital upon modern independence, while Sparta was rebuilt but not at all to the same extent or with quite the same prestige.

It’s complex, and there are other discussions to be had about other invasions, and the social ‘decline’ of Sparta in the Hellenistic era (as they saw it, at least), longer term economic factors during the later Roman/Byzantine empire, but I’ll leave these to others and I’d argue none of these were as clearly swiftly decisive.