S1·E38 Merlin

Crystal and the Centurions meet Professor Hartman at a medieval festival. He claims to have discovered the location of Merlin's tomb on an ancient map. They soon come under attack by Doc Terror's forces, who want Hartman's map. Terror wants Merlin's powers, and journeys to his tomb at Stonehenge to reawaken him. The Centurions arrive and protect Merlin from Terror, but he steals King Arthur's crown from the tomb. With the Crown, he summons the sword Excalibur, but it is taken by Hartman's assistant, who is descended from Morgan Le Fay. With Merlin's help, the Centurions try to retrieve Excalibur and defeat Terror.

Science Lesson: Stonehenge by Jake.