Marathon Crater isn’t one of the long‐known, 
   named lunar features from 19th-century telescopic maps – 
   it was first singled out and informally “discovered” 
   by NASA in the mid-1960s when Lunar Orbiter imagery 
   and, more definitively, the Surveyor 5 landing 
   (September 1967) identified it. So, very roughly, 
   think “around 1966–67.”