Depends on the time period you want. It was mainly Athens, but during the wars between Athens and Sparta, the latter had the title of capital when they won.
The Greek capital letter for Phi is Φ.
The Greek capital letter for Lamda is Λ.
The Greek capital letter for Xi is Ξ.
The Greek capital letter for Omega is Ω.
The Greek capital letter for Theta is Θ.
The Greek capital letter for Psi is Ψ.
The Greek capital letter for Delta is Δ.
The Greek capital letter for Sigma is Σ.
The Greek capital letter for Gamma is Γ.
The Greek capital letter for Pi is Π.
the capital of the greek eastern empire is Byzatine
In Greek capital letters, Heracles is spelled as ΗΡΑΚΛΗΣ.