This was SVN commit r10997.

binaries/data/mods/public/art/actors/props/units/heads/rome_helmet_mercellus.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<actor version="1">
+  <castshadow/>
+  <group>
+    <variant frequency="2" name="helmet-thracian-crest-feathers">
+      <mesh>props/helmet/helmet_thracian_5.dae</mesh>
+      <texture>props/helmet/mace_c.dds</texture>
+    </variant>
+  </group>
+  <material>player_trans.xml</material>
+</actor>

binaries/data/mods/public/art/actors/units/romans/hero_marcellus_r.xml

@@ -13,7 +13,7 @@
       </animations>
       <mesh>skeletal/m_tunic_short.dae</mesh>
       <props>
-        <prop actor="props/units/heads/rome_attic_bronze.xml" attachpoint="helmet"/>
+        <prop actor="props/units/heads/rome_helmet_mercellus.xml" attachpoint="helmet"/>
         <prop actor="props/units/heads/rome_head_hero_scipio.xml" attachpoint="head"/>
         <prop actor="props/units/weapons/gladus.xml" attachpoint="r_hand"/>
         <prop actor="props/units/shields/rome_parma_hero_2.xml" attachpoint="shield"/>