This is a question I often get asked and I think the answer is roughly between 1400 and 1500. I will do my best to back this up with some maps.
The first map, the one that says “mappa thaneti insule” along the top in latin dates from around 1400, different historians date it between 1380 and definitely before 1414 as it appears in the book by Thomas Elmham called “Historia Monasterii S Augustini Cantuariensis” Definitely and island then.
The second map, the one with the yellow and green watercolour shading on it, is a detail from a navigational chart for 1590. As you can see the Wantsum channel that used to separate the Isle of Thanet from the rest of the UK has silted up by then.
The third map, the one with the blue sea and green land, is one I drew to show the approximate situation back in 1400 and before.
In terms of books that explain about Thanet as an island, the main one and the one from which pretty much all of the information is derived is from 1736 “The History and Antiquities as well Ecclesiastical as Civil of the Isle of Tenet, in Kent The Second Edition, With Additions.” An original copy of this will set you back anything between £500 or £1,000 depending on the state it's in and whether it's got all of its pictures. A word of warning here: don't buy or read the first edition which I think was 1723 as it's only got about half the information in it. Here at Michaels bookshop in Ramsgate we do a cheap modern reprint of the 2nd edition, so you can always come into the bookshop and give it a browse.






























































