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From a sample of 15651 RR Lyrae with accurate proper motions in Gaia DR2, wemeasure the azimuthally averaged kinematics of the inner stellar halo between1.5 kpc and 20 kpc from the Galactic centre. We find that their kinematics arestrongly radially anisotropic, and their velocity ellipsoid nearly sphericallyaligned over this volume. Only in the inner regions $\lesssim$ 5 kpc does theanisotropy significantly fall (but still with $\beta >$ 0.25) and the velocityellipsoid tilt towards cylindrical alignment. In the inner regions, our sampleof halo stars rotates at up to 50 km s$^{-1}$, which may reflect the earlyhistory of the Milky Way, although there is also significant angular momentumexchange with the Galactic bar at these radii. We subsequently apply the Jeansequations to these kinematic measurements in order to non-parametrically inferthe azimuthally averaged gravitational acceleration field over this volume, andby removing the contribution from baryonic matter, measure the contributionfrom dark matter. We find that the gravitational potential of the dark matteris nearly spherical with average flattening $q_\Phi=$ 1.01 $\pm$ 0.06 between 5kpc and 20 kpc, and by fitting parametric ellipsoidal density profiles to theacceleration field, we measure the flattening of the dark matter halo overthese radii to be $q_\rho=$ 1.00 $\pm$ 0.09.

The Gravitational Force Field of the Galaxy Measured From the Kinematics of RR Lyrae in Gaia