Although started by Riccardo Freda (working as Robert Hampton), Caltiki, The Immortal Monster is usually credited to Mario Bava, who started out photographing the movie but took over directing as well early in its production. Whatever the particulars of the credits, the film's origins and execution have made it one of the most enduringly popular European sci-fi horror movies of its era. Although it's sometimes cited as being indebted to Irvin S. Yeaworth Jr.'s The Blob, Caltiki's real inspiration was almost certainly Val Guest's The Quatermass Experiment (aka The Creeping Unknown), which had been extremely popular in Italy. Caltiki incorporates a similar-looking monster, a manhunt for a stricken victim/carrier that parallels the center section of Guest's movie, and laboratory sequences depicting the monster's growth that are patterned directly after those in Guest's movie. There's even a nearly identical film-within-a-film segment that provides clues to the mystery early in the picture, exactly like Guest's movie. Caltiki's makers, however, have transposed the story away from space exploration -- a new-fangled and somewhat alien idea to most western and southern European countries (including Italy), which were far removed from rocket and missile programs -- and, instead, rather neatly folded together elements of ancient legend and archeology, subjects with which Italian audiences are familiar and comfortable. The result is a neat and compelling science fiction/horror amalgam, squeezing cosmology together with archeology and myth to create a genuinely fascinating and original thriller. Incorporating the ruins and mysteries left behind by the Mayans was an inspired idea, giving the European-made movie a wide reach into the prehistory of the Americas and imparting an appeal that was especially compelling in the United States as well as points south. Indeed, the plot even seems worthy of The X-Files or, better yet, Kolchak: The Night Stalker. Yes, the pacing is a little too brisk, the dubbing (done in New York, by Titras Studios, which dubbed many of the Italian movies of the period) is unfortunate in terms of some choices (such as the high, raspy voice giving to Max Gunther), the dialogue doesn't translate quite as well as one would wish -- and there are isolated moments when Caltiki resembles a pulsating pile of dirty rags. But the movie has a compelling core and sufficiently good photography (courtesy of Bava) and effects to make it worth watching and worth keeping, when and if it ever gets reissued on home video or DVD.