<p>This paper presents a procedure for estimating the minimum thickness of vaults and catenary arches to resist seismic in-plane horizontal loading. In order to define the shapes of the thrust lines that result from combining the self-weight of the arches and horizontal in-plane acceleration, an inverted hanging chain was used. The chain inclines the line by connecting its ends horizontally. Subsequently, iterative calculation help find the minimum thickness of the catenary arches with constant section that inscribe the defined thrust lines. This procedure was applied to different arches by considering ten values of horizontal acceleration. Consequently, graphs were drawn that relate the horizontal acceleration to the minimum thickness, contingent on the rise/span ratio of each arch, as well as the position of the hinges created in the collapse mechanism. Finally, the application is shown through the intersections of several catenary arches.</p>