A side lift spreader for lifting an intermodal transport container, the spreader comprising a main beam extending in a longitudinal direction; a pair of container locking arrangements (30a, 30b), each of said container locking arrangements (30a, 30b) being located at a respective longitudinal end of the spreader and being configured to be connected to a respective top corner casting (12a, 12b) of the container; and a container side support (32a, 32b) configured to support a longitudinal side of the container at a position vertically lower than the pair of container locking arrangements (30a, 30b), the spreader being characterized in that the main beam comprises a vertical carrier plate, the longitudinal axis of which extending in said longitudinal direction, the carrier plate having a first vertical height (H 1) and being made of steel plate having a first thickness (T 1); a C-beam extending in the longitudinal direction and comprising, as seen in cross-section, a first horizontal flange and a second horizontal flange interconnected by a vertical web portion, the C-beam having a second vertical height (H 2) lower than the first vertical height (H 1) and being made of steel plate having a second thickness (T 2) thinner than the first thickness (T 1), the first flange of the C-beam being welded to the carrier plate along a first longitudinal weld and the second flange of the C-beam being welded to the carrier plate along a second longitudinal weld such that the C-beam defines, together with the carrier plate, a closed channel beam with a first flange of the carrier plate extending vertically from the closed channel beam; and an elongate, inclined support plate extending along the longitudinal direction, the support plate being welded to the carrier plate along a third longitudinal weld, and to an outer face of the first flange of the C-beam along a forth longitudinal weld, the fourth longitudinal weld being located at a distance from the carrier plate. a main beam extending in a longitudinal direction; a pair of container locking arrangements (30a, 30b), each of said container locking arrangements (30a, 30b) being located at a respective longitudinal end of the spreader and being configured to be connected to a respective top corner casting (12a, 12b) of the container; and a container side support (32a, 32b) configured to support a longitudinal side of the container at a position vertically lower than the pair of container locking arrangements (30a, 30b), the spreader being characterized in that the main beam comprises a vertical carrier plate, the longitudinal axis of which extending in said longitudinal direction, the carrier plate having a first vertical height (H 1) and being made of steel plate having a first thickness (T 1); a C-beam extending in the longitudinal direction and comprising, as seen in cross-section, a first horizontal flange and a second horizontal flange interconnected by a vertical web portion, the C-beam having a second vertical height (H 2) lower than the first vertical height (H 1) and being made of steel plate having a second thickness (T 2) thinner than the first thickness (T 1), the first flange of the C-beam being welded to the carrier plate along a first longitudinal weld and the second flange of the C-beam being welded to the carrier plate along a second longitudinal weld such that the C-beam defines, together with the carrier plate, a closed channel beam with a first flange of the carrier plate extending vertically from the closed channel beam; and an elongate, inclined support plate extending along the longitudinal direction, the support plate being welded to the carrier plate along a third longitudinal weld, and to an outer face of the first flange of the C-beam along a forth longitudinal weld, the fourth longitudinal weld being located at a distance from the carrier plate.