Silla
Silla is a place named once in scripture and otherwise unidentified. It is fixed only by its relation to a second site — the house of Millo — and by the violent moment that put it on record.
On the Descent from Millo
The single occurrence sets Silla as the lower point on a road descending from the house of Millo, and pins it geographically by the conspiracy against Joash: "And his slaves arose, and made a conspiracy, and struck Joash at the house of Millo, [on the way] that goes down to Silla" (2Ki 12:20). The bracketed insertion clarifies that the conspirators did not strike Joash at Silla but on the road that runs down toward it. Silla itself remains a place of uncertain location, named only as the terminus that fixes the direction of the descent.