The Time Tunnel
Time travel is facilitated by time being portrayed as a static continuum, accessible at any point through the Time Tunnel as a corridor spanning its infinite reaches. When Senator Clark sees an image of the "Titanic" on the image screen in the course of episode one, he is told by Dr. Swain that he is seeing "the living past", and Althea Hall is told by Tony Newman that the past and the future are the same. The Time Tunnel is also a portal connecting the Time Tunnel "complex" with the same time periods in which Doug and Tony are located. Other people can also be relocated by the Time Tunnel from their time to another time as Machiavelli is switched from his own time to the time of the Gettysburg Campaign of 1863. Bringing people (other than Tony and Doug) to the present happens often in the series, but the only occasion in which Tony and Doug return to their own time occurs in "Merlin the Magician", when the great wizard uses magic to bring them home in suspended animation so he can instruct them to perform a mission for him.