Attested:  RC Insenos.  At the start of the British section of the Cosmography, in all three surviving manuscripts, is this piece of text: Iterum sunt in ipso [northern] oceano [islands] quae dicitur vectis malaca insenos taniatide.

Where:  Either the Selsey peninsula or Oxney island.  At present there are no islands off south-eastern England, between Vectis (Wight) and Taniatide (Thanet).  Dungeness was probably Malaca, but on its inland side, among marshes and water channels, Oxney was a definite island.  See, for example, the map below of how the Channel coast might have looked in Roman times, copied from page 196 of Lafaurie (1996), or here for how the coastline may have evolved over the centuries there, or here for a map of how the area may have looked like mediaeval times.  Despite all this, Oxney was not really in oceano and it seems slightly preferable to locate Insenos among the archipelago around the eastern end of the Solent, including Hayling Island, Thorney, Portsea, Bembridge Island (still separated from the rest of the Isle of Wight by a shipping channel when the Mary Rose sank), but especially the Selsey peninsula.

Name origin:  Uncertain.  PIE *senə- ‘apart, separated’ may also show up in the names Leugosena (Menai Strait) and Raxtomessasenua (Solent) suggesting a possible link to straits where low tide exposes a lot of sand.

Notes:  R&S suggested the Īle de Sein off the tip of Brittany, but that seems too far away, while the Goodwin Sands seem never to have been a real island.  Selsey may have been where Aelle came ashore at Cymenesora in AD 477.  Off Selsey lies a rocky reef called The Mixon, which may represent the southern tip of Selsey in Roman times, before sea levels rose.  It was much used over the centuries as a quarry conveniently accessible from the sea and may have contributed stone to the “palace” at Fishbourne, near Chichester.
[Lafaurie map here]
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Last edited: 24 August 2018