Make a sword
2 pieces of cardboard, scissors, aluminium foil, tape, dowel rod
Lie one piece of cardboard flat. Draw the sword on it with a pencil. A knight's sword typically has a long handle and a long blade that is even all around. Make the sword the size and shape that you desire. Use the first sword as a template to create a second sword on the other piece of cardboard.
Cut the swords out carefully with scissors. You should have two identical swords.
Flip the first sword over and use duct tape to secure a dowel rod going down the center of the sword. This will give the sword some shape so it won't flop over itself. Tape the second sword on the opposite side of the dowel rod to make the sword more durable.
Decorate the handle of the sword.
Wrap the entire blade of the sword with aluminum foil, shiny side out. This will make the blade look like real metal. Use clear tape to secure pieces that won't stay. Do a couple of layers of the foil if needed.