Which city became the first capital of independent Greece in 1828?

That would be the city of ???????, which has been anglicised in various ways, including Nafplio, Nauplia and Navplion. It lies on the Peloponnese peninsula, sitting on a smaller peninsula in the Argolic Gulf. It has been inhabited since ancient times, including by Egyptians, Byzantines, Franks, Venetians and Turks.

Nafplio features an elevated landform called the Acronauplia, further fortified by walls and other fortifications added and maintained by the long series of empires that once held it. Thanks to this, Nafplio was one of the last Ottoman-held strongholds to fall to the Greeks in the Greek War of Independence, after a blockade starved the Ottomans over the course of a year.

From its capture in 1827 until 1834, Nafplio was the provisional and then official capital of the First Hellenic Republic, a precursor to the modern Greek government. This was again thanks to its robust fortification. The capital was moved to Athens in 1834, where it remains to this day.

Oops, looks like the Greek characters didn't translate from the text box to the answer above. It should read Nu, alpha, upsilon with tonos, pi, lambda, iota, omicron.