Lattice tower for high-voltage overhead transmission lines (60, 90), having a lattice structure that includes: • a base anchored to the ground; • a top portion designed for anchoring first and second conductors of a high-voltage overhead transmission line; and • a body which extends between the base and the top portion; wherein said lattice tower comprises a grid high-voltage electric switching substation that includes: • GIS-technology-based switchgear equipment; • a first loop-in loop-out feeder connection that is - configured to connect the first conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; • a second loop-in loop-out feeder connection that is - configured to connect the second conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; and • a protection, command and control system arranged within the lattice structure, or in proximity to the base of said lattice structure; wherein the GIS-technology-based switchgear equipment is designed to be connected also to a user connection line; characterized in that the GIS-technology-based switchgear equipment is arranged within the base of the lattice structure. • a base anchored to the ground; • a top portion designed for anchoring first and second conductors of a high-voltage overhead transmission line; and • a body which extends between the base and the top portion; • GIS-technology-based switchgear equipment; • a first loop-in loop-out feeder connection that is - configured to connect the first conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; - configured to connect the first conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; • a second loop-in loop-out feeder connection that is - configured to connect the second conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; and - configured to connect the second conductors of the high-voltage overhead transmission line to the GIS-technology-based switchgear equipment, and - made by insulated cables or GIS-technology-based ducts, or by mixed solutions wherein a first portion is made by bare conductors and a second portion is made by insulated cables or GIS-technology-based ducts; and • a protection, command and control system arranged within the lattice structure, or in proximity to the base of said lattice structure;