2 added 733 characters in body
source | link

First the doubt is not whether Tiberias was walled, or not, it is a matter of whether Tiberias was settled from before the days of Yeshoshua Bin Nun this seen clearly on page 6a of the same Gemarra(English for those who need it).
  Likewise regardingThe Beit Yosef brings this in 688:4. There he brings the Rambam who says the sofek is whether Manhatten would have read on twoit was walled from the days of Joshua(even if an Islandnot whether or not it was considered walled). He also quotes the Gemarra in question.
The footnotes of the Tur HaMaor(number 1 on that page) say that there is a machloket in the Gemarra as what made the sofek, whether it was the sea as a wall(which is one option). The other issueoption is that it had to be settled by Jews fromTiberias is another city mentioned as walled(or not) in the Timebook of YehoshuaJoshua. As Assuming for now that it is the sea that causes the sofek, natural barriers(such as mountains and other things, which would also be a see) are spoken of in Mishnah Berurah 688688:92 of the Shulhan Arukh says, this is not an issue for any European or American city,(as well as the Tur and Beit Yosef). One of the issues we see there is no doubt that they were not inhabited by Jewsthe natural barrier cannot be more then a mil from what was settled in the time of Yehoshua Bin Nun. See the Mishneh Berurra seif katan 7 for further discussion on the distance. As far asSo to answer your question. Manhatten was not settled(by anyone) in the Greek citydays of KythnosYehoshua Bin Nun. If the Mishnah Berurra didn't consider Europe settled in those days, onecertainly North America was not either. Kythnos, would probably have to check with sometechnically be possible, if the city covered enough of the older Greek/Byzantine Poskim to see what they write regardingisland that no edge of it, if there was evermore than a Jewish presence theremil from the Ocean. However looking at maps, as I am not sure that it would fit the Mishnar Berurra's definitionseems to actually a collection of "far" from Eretz Yisrael(though it might)small villages on a rather large island, and thus also would not work.

First the doubt is not whether Tiberias was walled, or not, it is a matter of whether Tiberias was settled from before the days of Yeshoshua Bin Nun this seen clearly on page 6a of the same Gemarra(English for those who need it).
  Likewise regarding whether Manhatten would have read on two days(even if an Island was considered walled) the other issue is that it had to be settled by Jews from the Time of Yehoshua. As the Mishnah Berurah 688:9 says, this is not an issue for any European or American city, as there is no doubt that they were not inhabited by Jews in the time of Yehoshua Bin Nun. As far as the Greek city of Kythnos, one would probably have to check with some of the older Greek/Byzantine Poskim to see what they write regarding it, if there was ever a Jewish presence there, as I am not sure that it would fit the Mishnar Berurra's definition of "far" from Eretz Yisrael(though it might).

First the doubt is not whether Tiberias was walled, or not, it is a matter of whether Tiberias was settled from before the days of Yeshoshua Bin Nun this seen clearly on page 6a of the same Gemarra(English for those who need it). The Beit Yosef brings this in 688:4. There he brings the Rambam who says the sofek is whether it was walled from the days of Joshua(not whether or not it was walled). He also quotes the Gemarra in question.
The footnotes of the Tur HaMaor(number 1 on that page) say that there is a machloket in the Gemarra as what made the sofek, whether it was the sea as a wall(which is one option). The other option is that Tiberias is another city mentioned as walled(or not) in the book of Joshua. Assuming for now that it is the sea that causes the sofek, natural barriers(such as mountains and other things, which would also be a see) are spoken of in 688:2 of the Shulhan Arukh(as well as the Tur and Beit Yosef). One of the issues we see there is that the natural barrier cannot be more then a mil from what was settled in the time of Yehoshua Bin Nun. See the Mishneh Berurra seif katan 7 for further discussion on the distance. So to answer your question. Manhatten was not settled(by anyone) in the days of Yehoshua Bin Nun. If the Mishnah Berurra didn't consider Europe settled in those days, certainly North America was not either. Kythnos, would technically be possible, if the city covered enough of the island that no edge of it was more than a mil from the Ocean. However looking at maps, it seems to actually a collection of small villages on a rather large island, and thus also would not work.

1
source | link

First the doubt is not whether Tiberias was walled, or not, it is a matter of whether Tiberias was settled from before the days of Yeshoshua Bin Nun this seen clearly on page 6a of the same Gemarra(English for those who need it).
Likewise regarding whether Manhatten would have read on two days(even if an Island was considered walled) the other issue is that it had to be settled by Jews from the Time of Yehoshua. As the Mishnah Berurah 688:9 says, this is not an issue for any European or American city, as there is no doubt that they were not inhabited by Jews in the time of Yehoshua Bin Nun. As far as the Greek city of Kythnos, one would probably have to check with some of the older Greek/Byzantine Poskim to see what they write regarding it, if there was ever a Jewish presence there, as I am not sure that it would fit the Mishnar Berurra's definition of "far" from Eretz Yisrael(though it might).