Llanidan is a community in the south of Anglesey, Wales which includes the village of Brynsiencyn (). The parish is along the Menai Strait, about 4 miles north-east of Caernarfon (across the strait). The parish church of St Nidan is near the A4080 highway, a little to the east of Brynsiencyn. The ruins of an earlier parish church survive. History Possible site of Roman invasions On the basis of field names it has been suggested that the Roman army under Suetonius Paulinus landed here in 60, and again in 78 under Agricola, overcoming the Ordovices of north-west Wales and Anglesey, at a spot known as Bryn Beddau, (Hill of Graves in Welsh). In 1867 it was suggested that the local field names "Maes Hir Gad" (Area of long battle) and "Cae Oer Waedd" (Field of cold or bitter lamentation) may indicate the site of these battles Roman coastal settlement Near Tai Cochion house, excavation and geophysical survey has revealed part of a Roman settlement of unusual layout, and on the opposite side of the Menai Strait to the Roman fort at Segontium. This may mark the main crossing of the Menai Strait. A trading settlement would have been likely at such a point. Geophysical survey indicates a road of typical Roman construction, 600 metres long and 8 metres wide, with several side branches, running slightly north of east from Tai Cochion house to the shore of the Menai Strait. The roads were flanked by a series of small enclosures, with typical dimensions of about 20m x 40m. Many of the enclosures contained fairly clear, rectangular anomalies interpreted as buildings, with typical dimensions of around 16m x 8m. About 25 possible buildings were detected by the survey. Most appeared to be rectangular, possibly with internal subdivisions. A few seemed to be more complex with extensions or additional rooms. The layout, with a central road flanked by plots containing rectangular buildings, is similar to Roman villages and small towns such as Sedgefield. This arrangement has no defences and is otherwise unlike the military Roman sites in Wales, nor does it resemble the native defended settlements with their roundhouses and irregular outlines, nor the occasional villas; it suggests a previously unknown level of civilian Romanization in the remote west of the province. Two other similar layouts in Wales are suggested by aerial photography; on the opposite side of the Menai Strait, adjacent to