The Wikipedia article on Caracalla says:
Dio maintains that one purpose for Caracalla issuing the edict was the desire to increase state revenue; at the time Rome was in a difficult financial situation and needed to pay for the new pay raises and benefits conferred on the military. The edict widened the obligation for public service and gave increased revenue through the inheritance and emancipation taxes which, at the time, only had to be paid by Roman citizens.
I've been told that the resulting revenue was then stored in the Temple of Saturn.
How did it get there? What was the procedure? Did the Emperor or Senate send agents to the provinces to collect the inheritance tax, or was it part of the general system of tax farming, or what? How was the collected revenue transported? Were special guards appointed to protect the wagons (?) filled with gold and silver on their way to Rome?