From Hadronic Cross Section to the measurement of the Vacuum Polarization at KLOE: a fascinating endeavour

The KLOE experiment at the $\varphi -factory$ DA$\mathrm{\Phi }$NE in Frascati is the first to have employed Initial State Radiation (ISR) to precisely determine the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}(\gamma )$ cross section below 1 GeV. Such a measurement is particularly important to test the Standard Model (SM) calculation for the $(g-2)$ of the muon, where a long standing 3$\sigma$ discrepancy is observed. I will review the ISR activity in KLOE in the last 18 years from the measurement of the hadronic cross section to the first direct determination of the time-like complex running $\alpha (s)$ in the region below 1 GeV.