what axe is suitable?

[Felis]

Lv 49 Axe is good enough for Castrum.
After Castrum you can start the relic quest to get a ilevel 80 axe (first relic) and ilevel 90 axe (first upgrade of the relic).
If you want a level 50 axe then buy that one you would need for the relic quest afterwards. For the WAR relic this should be the Barbarian's Bardiche (ilevel55)

[Seryl199]

Lv 49 Axe is good enough for Castrum.
After Castrum you can start the relic quest to get a ilevel 80 axe (first relic) and ilevel 90 axe (first upgrade of the relic)

This, if you'd like to GC rank up after Castrum, you can get the ilvl 55 GC weapon to ease your entry into level 50 content, but you'll quickly replace it with a primal dropped weapon, and a relic soon after

[Ashkendor]

Lv 49 Axe is good enough for Castrum.
After Castrum you can start the relic quest to get a ilevel 80 axe (first relic) and ilevel 90 axe (first upgrade of the relic).
If you want a level 50 axe then buy that one you would need for the relic quest afterwards. For the WAR relic this should be the Barbarian's Bardiche (ilevel55)

Pretty sure you have to finish Praetorium to access A Relic Reborn.