Apparatus comprising an endovascular stent-graft system, which comprises: a fenestrated stent-graft, which includes first and second end portions (24, 26) and a central portion disposed longitudinally therebetween, and which comprises a fenestrated support structure and a fenestrated covering element, which is securely attached to and covers at least a portion of the fenestrated support structure, wherein the fenestrated support structure and the fenestrated covering element are shaped so as to together define first and second lateral apertures (40, 42) in the central portion, which apertures (40, 42) face in generally radially opposing directions, when the fenestrated stent-graft is in a radially-expanded state thereof; and a crossing stent-graft, which includes first and second end portions (44, 46) and a central portion disposed longitudinally therebetween, and which comprises a crossing support structure and one or more crossing covering elements, which are securely attached to and at least partially cover the first and the second end portions, (44, 46), such that the central portion is at least partially uncovered when the crossing stent-graft is in a radially-expanded state thereof, wherein the fenestrated and the crossing stent-grafts (20, 22) are sized and shaped such that, when the crossing stent-graft is disposed through the first and the second lateral apertures (40, 42) such that the central portion of the crossing stent-graft is within the central portion of the fenestrated stent-graft, the first and the second end portions (44, 46) of the crossing stent-graft (a) pass through the first and the second lateral apertures (40, 42), respectively, and (b) when the fenestrated and the crossing stent-grafts (20, 22) are in their radially-expanded states, form blood-impervious seals with the first and the second lateral apertures (40, 42), respectively, such that interior spaces defined by all of the following are in fluid communication with one another: the first and the second end portions (24, 26) and the central portion of the fenestrated stent-graft, and the first and the second end portions (44, 46) and the central portion of the crossing stent-graft. a fenestrated stent-graft, which includes first and second end portions (24, 26) and a central portion disposed longitudinally therebetween, and which comprises a fenestrated support structure and a fenestrated covering element, which is securely attached to and covers at least a portion of the fenestrated support structure, wherein the fenestrated support structure and the fenestrated covering element are shaped so as to together define first and second lateral apertures (40, 42) in the central portion, which apertures (40, 42) face in generally radially opposing directions, when the fenestrated stent-graft is in a radially-expanded state thereof; and a crossing stent-graft, which includes first and second end portions (44, 46) and a central portion disposed longitudinally therebetween, and which comprises a crossing support structure and one or more crossing covering elements, which are securely attached to and at least partially cover the first and the second end portions, (44, 46), such that the central portion is at least partially uncovered when the crossing stent-graft is in a radially-expanded state thereof, wherein the fenestrated and the crossing stent-grafts (20, 22) are sized and shaped such that, when the crossing stent-graft is disposed through the first and the second lateral apertures (40, 42) such that the central portion of the crossing stent-graft is within the central portion of the fenestrated stent-graft, the first and the second end portions (44, 46) of the crossing stent-graft (a) pass through the first and the second lateral apertures (40, 42), respectively, and (b) when the fenestrated and the crossing stent-grafts (20, 22) are in their radially-expanded states, form blood-impervious seals with the first and the second lateral apertures (40, 42), respectively, such that interior spaces defined by all of the following are in fluid communication with one another: the first and the second end portions (24, 26) and the central portion of the fenestrated stent-graft, and the first and the second end portions (44, 46) and the central portion of the crossing stent-graft.