Caesar, Gallic War
2.17 (an ancient practice of the Nervii; tr. H.J. Edwards):
Having no strength in cavalry (for even to this day they care naught for that service, but all their power lies in the strength of their infantry), the easier to hamper the cavalry of their neighbours, whenever these made a raid on them, they cut into young saplings and bent them over, and thus by the thick horizontal growth of boughs, and by intertwining with them brambles and thorns, they contrived that these wall-like hedges should serve them as fortifications which not only could not be penetrated, but not even seen through.
Cum equitatu nihil possent (neque enim ad hoc tempus ei rei student, sed, quidquid possunt, pedestribus valent copiis), quo facilius finitimorum equitatum, si praedandi causa ad eos venissent, impedirent, teneris arboribus incisis atque inflexis crebrisque in latitudinem ramis enatis et rubis sentibusque interiectis effecerant, ut instar muri hae saepes munimenta praeberent, quo non modo non intrari, sed ne perspici quidem posset.
Strabo 4.3.5 (tr. Horace Leonard Jones):
Both the country of the Morini and that of the Atrebatii and Eburones resemble that of the Menapii; for much of it, though not so much as the historians have said (four thousand stadia), is a forest, consisting of trees that are not tall; the forest is called Arduenna. At the time of hostile onsets they used to intertwine the withes of the brushwood, since the withes were thorny, and thus block the passage of the enemy.
ἐμφερὴς δ᾿ ἐστὶ τῇ τῶν Μεναπίων ἥ τε τῶν Μορινῶν καὶ ἡ τῶν Ἀτρεβατίων καὶ Ἐβουρώνων· ὕλη γάρ ἐστιν οὐχ ὑψηλῶν δένδρων πολλὴ μέν, οὐ τοσαύτη δὲ ὅσην οἱ συγγραφεῖς εἰρήκασι, τετρακισχιλίων σταδίων, καλοῦσι δ᾿ αὐτὴν Ἀρδουένναν. κατὰ δὲ τὰς πολεμικὰς ἐφόδους συμπλέκοντες τὰς τῶν θάμνων λύγους, βατώδεις οὔσας, ἀπέφραττον τὰς παρόδους.