In aerial imagery captured via Google Earth in January 2017, the southern sector of the park reveals cropmarks, those subtle variations in vegetation that betray buried or disturbed ground, tracing the distinctive crenellated zigzag pattern of First World War practice trenches. A second set of similar lines appears roughly seventy metres to the north. Taken together, they suggest a more systematically laid-out trench system than a single incidental feature would imply.

Practice trenches were a routine feature of military preparation during the First World War. Soldiers needed to understand how to move through, construct, and defend trench systems before reaching the Western Front, and purpose-dug training trenches were created at numerous sites across Britain and Ireland. The crenellated or zigzagging plan was not decorative; it was functional, designed to limit the blast radius of shells and prevent an enemy who entered one section from firing directly along the full length. That this pattern appears in the Phoenix Park is perhaps less surprising than it sounds, given the park's long association with the British military in Ireland, though the specific history of this particular feature has not been extensively documented. The site was identified and recorded by Caimin O'Brien, working from details supplied by John Mulligan, and uploaded to the record in May 2020.

The cropmarks are not visible at ground level, which makes this an unusual case of a site that is technically accessible but effectively invisible without aerial perspective. A visitor walking the southern sector of the park near Chapelizod would find nothing obviously remarkable underfoot, just open grassland. The features are best appreciated by examining the 28 January 2017 Google Earth orthoimage, which clearly shows the crenellated lines in the soil patterning. If you visit in a dry summer, when differential moisture in disturbed ground tends to produce the strongest cropmark effects, you might find yourself standing directly above the buried outlines of trenches dug by men rehearsing for a war that would kill so many of them, with no indication at all that the ground beneath your feet holds any record of that preparation.