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This is a view of a pool that, according to the excavator, was used for the soaking of Balsam branches.
The balsam plantations at Jericho were world famous and this precious commodity was shipped all over the Roman World. To harvest it I believe that usually not-too-deep slits were cut into the branches of the bush with either a sharp bone or piece of glass—never with a metal knife. The sap that came out was processed for its scent.
Evidently, another method included the cutting and soaking of crushed branches, in a pool such as this, but I am not certain how that process actually worked. I am guessing that the finished product, although valuable, was not as good quality as that produced by the method described above.
See Netzer, Ehud, and Rachel Laureys–Chachy. The Architecture of Herod, the Great Builder. Grand Rapids: Baker Academic, 2008, pp. 42–80.