The word amontonaba is the imperfect form of amontonar in the first person singular. There are other translations for this conjugation.
See the full amontonar conjugation

amontonar

La gente las recogía y las amontonaba, y el hedor de las ranas llenaba el país.
They were piled into heaps, and the land reeked of them.
La nieve se amontonaba cada vez más alta frente a la puerta mientras progresaba la ventisca.
Snow drifted higher and higher in front of the door as the blizzard progressed.
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