Michael Short (1990) claims the persistent 5/4 meter in Gustav Holst's Mars is the "most striking feature" in what some call "the most ferocious piece of music in existence", Short (123-24). But the literature has not thoroughly addressed Mars's interesting metrical features. In a broad overview of rhythm and meter in Holst's music, Short briefly mentions the 5/4 ostinato and the hemiola created by the superimposition of 5/2 over two bars of 5/4, but he does not detail the metric properties of Mars any further (349-66). Richard Greene (1995) briefly suggests the 5/4 ostinato is a metaphor for battle, but he does not detail the extent of this metaphor (69). I claim that the percussive ostinato in 5/4 time is not just a metaphor for battle, but the meter itself participates in a battle throughout the movement. The battle primarily involves the interplay between 5/4 and 5/2 during the emergence of 5/2 in the context of a 5/4 meter; superimposition of 5/2 over 5/4; and alternation between 5/4 and 5/2. Drawing from Harald Krebs's (1997) metric displacement, Richard Cohn's (2001) metric states, and John Roeder's (1994) pulse streams, I explore all of these interactions in the metric battle of Mars.