There are no earthworks to see, no signage pointing to a lost feature, and no obvious reason to look twice at the site. Yet before this church was extended, archaeologists found evidence suggesting that a significant earthen mound once occupied exactly this spot, and that people were active here during the 13th or 14th centuries.

Flanagan noted as far back as 1984 that a mound had formerly stood on the present site of St Sylvester's church. When test excavations were carried out in advance of a church extension, first under licence 10E0426 and then under licence 11E0326, the digs began to fill in the picture. The earlier investigation identified a small pit or drainage gully and a silty deposit that may belong to the medieval period. The follow-up work went further, uncovering medieval structural remains, ditch pits, and masonry walls from the 18th or 19th century. Medieval pottery recovered during these excavations points to meaningful activity on or near the site during the 1200s or 1300s. Archaeologists have raised the possibility that the pottery relates to the mound itself, which may have been either a motte, an earthen mound raised as a fortification in the Norman period, or a rath, a circular earthen enclosure used as a defended farmstead in earlier Irish society. Either way, the evidence suggests the site was occupied over a considerable stretch of time.

St Sylvester's church sits within Malahide village and remains an active parish church, so access to the grounds is subject to the usual courtesies extended to a functioning place of worship. There is nothing visible at ground level to indicate any earthwork ever existed here; the archaeological interest lies entirely beneath the surface and in the excavation records. For those who find themselves in Malahide and want to think about the layers beneath the ordinary, it is worth knowing that the unremarkable ground around the church has already yielded medieval pottery, structural traces, and the ghost of a mound that no longer shows itself.