On the structure of $C_0$-semigroups of holomorphic Carath\'eodory isometries We extend Vesentini's description of the infinitesimal generators of strongly continuous one-parameter semigroups of holomorphic Carat\'oodory isometries of the unit ball of a complex Hilbert space to the setting of reflexive Cartan factors. Our treatment is based on intensive use of joint fixed points along with Kaup type ideas with partial vector fields of second degree. In particular we establish closed formulas for the Hilbert space case in terms of spectral resolutions of skew self-adjoint dilations related to the Reich-Shoikhet non-linear infinitesimal generator. We also provide partial results toward a Hille-Yosida type theory for holomorphic self-maps of bounded domains in Banach spaces.