Until this post, never heard of it.
" The Newport Tower, located in Touro Park (Newport, Rhode island) , is considered the single most enigmatic and puzzling structure to be found in the United States. Many scholars here and abroad have written extensively about its probable builders. They all agree that it was not erected by the American Indians. Its architectural characteristics indicate a style from Europe or the Near East. "
There is a quite detailed exploration of the Newport Tower at:
http://www.neara.org/CARLSON/newporttower.htm
If you have some time to read it all...
There is a rumor about the tower being built by the Chinese...about 100 years prior to Columbus arriving in the US. A rather difficult story to believe...but the design and effort...leave one to question all possible scenarios.
http://www.knowledgerush.com/kr/encyclopedia/Newport_Tower/
“To date no hard evidence supporting the Norse explanation has been found”