They think probably payroll.
Beats a bag of salt!
Maybe the army had to make a hasty retreat,,,,,,,,,,,,,,,,,,,,
Are you alluding to the fact that the word "salary" comes from the Latin word salarium, meaning "salt-money?" Because Roman soldiers were famously paid a portion of their wages in salt?
Depending upon how debased the currency was at the time, an equal weight of salt might have been more valuable.
Regards,
From the CNN link:
The initial hypothesis is that the coins were to be used to pay taxes to the Roman empire, according to Spanish newspaper El Pais.