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We examine the circulation forced by a gradient in surface temperature, known as horizontal convection, in a rectangular basin under planetary rotation. Direct numerical simulations are carried out to examine the problem in a closed rectangular basin that is heated over half of the base and cooled over the other half. Three Rayleigh numbers are considered, Ra= 7.4× 108, 7.4× 1011 and 7.4× 1012, and Coriolis parameter is varied to give Ekman numbers in the range E= 6.4× 10− 8− 1.6× 10− 5. Other governing parameters are the Prandtl number Pr= 5 and vertical-to-length and horizontal-to-length aspect ratios, A= 0.16 and C= 0.24 respectively. The influence of rotation on flow dynamics and heat transfer depends on the natural Rossby number Ro= U/fL=(E/Pr)(RaE) 2/3 where U is the flow velocity in the thermal boundary layer that forms adjacent to the forced surface and f is the Coriolis parameter. When the system is in a rapidly rotation regime (Ro< 0.1) the flow is characterised by geostrophic balance in the thermal boundary layer. The heat transfer, expressed as a Nusselt number, decreases with rotation but increases with buoyancy forcing as Nu∼(RaE) 1/3. A range of length scales are present in the rotating system that are associated with structures such as domainscale gyres and full-depth convective vortices.