Military post offices on the Salonica front. The period between Decembre 1917 and February 1918 the post office "TRESOR ET POSTES*504" cancel all the stamps. 2 covers: 1st fr. with 5c.+2x10c. and cancelled with "TRESOR ET POSTES*504*5 12 17" (earliest date seen of this chanche) and 2nd fr. with 25c. and canc. with "TRESOR ET POSTES*504*9 2 18" (Latest date seen). RRR.