Why was Constantinople so hard to conquer?

entering that problem on the tube you may come up with an answer

sir thomas more, venerated in the catholic church as saint thomas more, was an english lawyer, social philosopher, author, statesman, and noted renaissance humanist. he was also a councillor to henry viii, and lord high chancellor of england from october 1529 to 16 may 1532.

this isn't a question and if you're going to list things be kind and use commas.

in 1989, tiananmen square in beijing was the site of china’s main industries. china’s government headquarters. -pro-democracy demonstrations. (second choice)