The expression comes in a number of suttas from AN (AN 5.54, AN 5.78 etc.)
It goes like this:
bhayaṃ hoti aṭavisaṅkopo, cakkasamārūḷhā jānapadā pariyāyanti.
Translations vary a lot
there is peril, turbulence in the wilderness, and the people of the countryside, mounted on their vehicles, flee on all sides.
there is danger & an invasion of savage tribes. Taking power, they surround the countryside.
The commentary says:
‘aṭavisaṅkopo’ ti aṭaviyā saṅkopo. aṭavīti cettha aṭavivāsino corā veditabbā. yadā hi te aṭavito janapadaṃ otaritvā gāmanigamarājadhāniyo paharitvā vilumpanti, tadā aṭavisaṅkopo nāma hoti, taṃ sandhāyetaṃ vuttaṃ.
I don’t feel comfortable enough to provide an exact translation, but it says it should be understood as thieves dwelling in the forest, who come out of the forest, invade villages and towns and plunder them
ven. BB: turbulence in the wilderness (saGkopayati in Sankrit means ’ become agitated, excited or angry’)
ven. TB: an invasion of savage tribes (? I guess this is due to those people coming from the forest, translating saṅkopo as ‘savage’)
‘cakkasamārūḷhā’ ti ettha iriyāpathacakkampi vaṭṭati yānacakkampi. bhayasmiṃ hi sampatte yesaṃ yānakāni atthi, te attano parikkhārabhaṇḍaṃ tesu āropetvā palāyanti. yesaṃ natthi, te kājena vā ādāya sīsena vā ukkhipitvā palāyantiyeva. te cakkasamārūḷhā nāma honti.
When the danger arrives, those who have a cart put their important belongings in it and run away, and those who have none take carrying poles or carry their belongings on their head and run away.
ven. BB: mounted on their vehicles
ven. TB: Taking power (? probably a non-litteral interpretation with cakka - the wheel - as symbol of power)
‘pariyāyantī’ ti ito cito ca gacchanti.
Apparently, this means that they go ‘here and there’ (wherever they can).
ven. BB: they flee on all sides
ven. TB: they surround the countryside (this apparently takes janapadā as what should be an accusative, which it is not, it seems).