The Relativistic Field Theory of Primes (RFTP) is a self-contained arithmetic fieldtheory in which the primes, modular forms, and monstrous moonshine are promoted to thedynamical degrees of freedom of a clutched adelic bundle over the compactified modularcurve X(1). The theory begins with the Eisenstein series E4(τ ), E6(τ ), and E12(τ ) and therigorously derived Ramanujan—Serre congruence τ (n) ≡ σ11(n) (mod 691), which is elevatedto the primary topological defect injecting the delta source ρsource =65520691 δj(τ)(P) into theArakelov Poisson equation. This single defect sources a shared curvature potential Veff(r, ϕ)felt identically by timelike soliton geodesics and null photon rays, generating a conservedRunge—Lenz vector and an SO(4) symmetry that unifies gravitational and electromagneticscales.A least-arithmetic-action functional S[Φ] on the Monster vertex operator algebra V♮yields a self-adjoint radial Dirac operator D on the clutched bundle whose spectrum interpolates the Balmer series and the critical-line zeta zeros. The theory realizes a Connesspectral triple (AVOA, Hsoliton, D), Einstein—Cartan gravity with χ11-sourced torsion, andphoton propagation via explicit multi-field WKB ray-tracing. Modular invariance underSL(2,) is the arithmetic skeleton: it preserves the characteristic bending speed p|d2r/ds2|,the Runge—Lenz vector, the gravitational constant GA = 65520/(8π · 691), the speed ofcausality cA, all spectra, scattering cross-sections, Einstein A/B coefficients, vacuum energy,dark-energy equation of state, and cosmological constant. The wave/ray duality explainsthe integer 3 (triality compactness of the ray limit) and the transcendental tail of π (infinitedimensional wave phase space). The Gutzwiller trace formula over modular periodic orbitslinks the primes to the zeta zeros, while compactness, discreteness, and finiteness of theclutched bundle enforce ultraviolet finiteness at the Planck scale lP .All constants and observables emerge purely arithmetically from the single master functional and the 691 defect, with no external parameters. RFTP therefore provides a parameterfree unification in which modular symmetries dictate the observable universe.