Hi Artur,

     It probably refers to some contraption surrounded by a host of serpents.  Serpents as guardians of hidden underground treasures is a reasonably common idea in Indian literature.

Madhav 

On Mon, Sep 12, 2016 at 8:24 AM, Artur Karp <karp@uw.edu.pl> wrote:

Dear Madhav, 

The PTS,s Pali-English Dict.:

Vāḷa - [cp. late Sk. vyāḍa, see Geiger, P. Gr. § 54⁶] I. a snake Vism 312 (so read for vaḷa).- 2. a beast of prey [...] vāḷa-miga, a beast of prey, predaceous animal, like tiger, leopard, etc. [...]

When in search for the Elixir of immortality Garuda enters the underworld, he kills two serpents hidden under the [eternally] revolving wheel. (Mbh. I, 29. 3-9). 

When the relics of the Buddha are hidden by Ajatasattu in the underground chamber, Vissakamma places over them, for their defence the [eternally] revolving vāḷa–saṅghāṭa–yanta.

If vāḷa would mean "snake, serpent", then this could be one of the tropes linking both the narrations.

Yanta means "contrivance, artifice, instrument, machine, mechanism" - in what way could it be constructed/pegged together - using serpents? Ataching it to serpents? Giving it a serpentine look?

Artur