In SMG feminine nouns corresponding to the Ancient Greek third declension have stems ending in -σ- (αίτηση, θέση) or some consonant combined with sigma such as ξ (λέξη) or ψ (σκέψη) with exceptions δύναμη and πόλη. The nominative and genitive singular forms vary between ancient and modern endings even in SMG, with η πόλις and της πόλεως almost as frequent as η πόλη and της πόλης.
The modern nominative ending in ita derives from the old accusative:
την πόλιν > την πόλη > η πόλη