For Damascus steel and Greek Fire we almost certainly still have the knowledge. We just lack a document to tell us that "Greek Fire" matches formula #44 of napalm specifically, or what specific process an ancient smith actually followed.
For the spaceships, no, we have the plans, but they're long obsolete. They're made for ancient, manual equipment nobody uses anymore, and old materials that have since been improved on. We technically could dig up and restore ancient manual milling machines, recruit retired engineers and special order obsolete materials and parts, but what for? Unless you're engaging in experimental archaeology what you want is a rocket, not the rocket that has a nostalgic feel to it, and it'd make far more sense to make one with modern methods.
For Damascus steel and Greek Fire we almost certainly still have the knowledge. We just lack a document to tell us that "Greek Fire" matches formula #44 of napalm specifically, or what specific process an ancient smith actually followed.
For the spaceships, no, we have the plans, but they're long obsolete. They're made for ancient, manual equipment nobody uses anymore, and old materials that have since been improved on. We technically could dig up and restore ancient manual milling machines, recruit retired engineers and special order obsolete materials and parts, but what for? Unless you're engaging in experimental archaeology what you want is a rocket, not the rocket that has a nostalgic feel to it, and it'd make far more sense to make one with modern methods.