Translation of "Tropel" in English

Já me encontrava perto da saída, / já passado o perigo acreditava, / quando ouvimos um súbito tropel. / Lobrigando na treva, meu pai grita: / “Filho, apressa-te, filho, estão chegando! / Lampejo de armas vejo e escudos reluzentes.”

And now I neared the gates, and thought my flight / achieved, when suddenly a noise we hear / of trampling feet, and, peering through the night, / my father cries, "Fly, son, the Greeks are near; / they come, I see the glint of shield and spear, / fierce foes in front and flashing arms behind."