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Andromeda is our nearest neighbouring disk galaxy and a prime target fordetailed modelling of the evolutionary processes that shape galaxies. Weanalyse the nature of M31's triaxial bulge with an extensive set of N-bodymodels, which include Box/Peanut (B/P) bulges as well as initial classicalbulges (ICBs). Comparing with IRAC 3.6$\mu m$ data, only one model matchessimultaneously all the morphological properties of M31's bulge, and requires anICB and a B/P bulge with 1/3 and 2/3 of the total bulge mass respectively. Wefind that our pure B/P bulge models do not show concentrations high enough tomatch the S\'ersic index ($n$) and the effective radius of M31's bulge.Instead, the best model requires an ICB component with mass $M^{\rmICB}=1.1\times10^{10}{\rm M_{\odot}}$ and three-dimensional half-mass radius$r_{\rm half}^{\rm ICB}$=0.53 kpc (140 arcsec). The B/P bulge component has amass of $M^{\rm B/P}=2.2\times10^{10}{\rm M_{\odot}}$ and a half-mass radius of$r_{\rm half}^{\rm B/P}$=1.3 kpc (340 arcsec). The model's B/P bulge extends to$r^{\rm B/P}$=3.2 kpc (840 arcsec) in the plane of the disk, as does M31'sbulge. In this composite bulge model, the ICB component explains the velocitydispersion drop observed in the centre within $R<$190 pc (50 arcsec), while theB/P bulge component reproduces the observed rapid rotation and the kinematictwist of the observed zero velocity line. This model's pattern speed is$\Omega_p$=38 km/s/kpc, placing corotation at $r_{\rm cor}$=5.8 kpc (1500arcsec). The outer Lindblad resonance (OLR) is then at $r_{\rm OLR}$=10.4kpc,near the 10kpc-ring of M31, suggesting that this structure may be related tothe bar's OLR. By comparison with an earlier snapshot, we estimate that M31'sthin bar extends to $r_{\rm bar}^{\rm thin}\sim$4.0 kpc (1000 arcsec) in thedisk plane, and in projection extends to $R_{\rm bar}^{\rm thin}\sim$2.3 kpc(600 arcsec).

Andromeda chained to the Box -- Dynamical Models for M31: Bulge & Bar