Callicrătes in Harpers Dictionary of Classical Antiquities
An architect, who, in conjunction with Ictinus, built the Parthenon at Athens, and who undertook also to complete the Long Walls termed σκέλη (Pericl. c. 13). He appears to have flourished about B.C. 440.
Kallikrates in Wikipedia
Kallikrates (also spelled Callicrates) was an ancient Greek architect active in the middle of the fifth century BCE. He and Iktinos were architects of the Parthenon (Plutarch, Pericles, 13) . An inscription identifies him as the architect of "the Temple of Nike" in the Sanctuary of Athena Nike on the Acropolis (IG I3 35). The temple in question is either the amphiprostyle Temple of Athena Nike now visible on the site  or a small-scale predecessor (naiskos) whose remains were found in the later temple's foundations.. An inscription identifies Kallikrates as one of the architects of the Classical circuit wall of the Acropolis (IG I3 45), and Plutarch further states (loc cit) that he contracted to build the Middle of three amazing walls linking Athens and Piraeus. Aimee Hewitt stated in her recent book that Kallikrates was a man of great standing within Athens and was very important member of the Areopagus Council.