We still don't know who built it.

Inigo Jones, who surveyed Stonehenge in 1655, was so impressed by the skill of its builders that he assumed they were Romans and a century later John Wood, who shared Jones's assumption, based his great neo-Classical Circus in Bath on Jones's plan of Stonehenge.

And there's the problem with the Newport Tower claim. The petition says that this 'county palatine' is to include the island in question and some of the adjoining continent, and is at 39 degrees latitude and 150 miles north of James City. Newport is at 41.27 degrees latitude and much more than 150 miles north of James City. The area in the petition is the area of the Delaware/Maryland peninsula, and the tower in the ‘commodities’ document, whether proposed or existing, is not in Rhode Island.

Shortly after this Plowden revised his petition, renaming the island ‘Isle Plowden’, increasing the number of prospective settlers, changing the name of the colony to New Albion and asking for a grant 120 miles to a side to include all other small islands between 39 and 40 degrees latitude. A patent was issued on July 24, 1632, although the charter was not forthcoming until 1634. This was a feudal charter held by Plowden by knight service of Charles I’s Irish crown (which meant the king could profit from it), allowing Plowden to grant titles, etc. which he liberally did (creating one of his sons ‘High Admiral and Baron of Roymount’.

However, nothing came of it. Plowden did not leave for New Albion until 1642, spending his time in lawsuits with tenants, creditors, debtors and his wife while Swedes were busy colonising along the Delaware River. Rather than go to New Albion, in fact, he went to Virginia. An attempt to go to New Albion was then met with mutiny, and that was the end of Plowden’s only known attempt to settle the land he had been granted. He spent the rest of his life (he died in 1859) in lawsuits and conflict with his family.

Once the Tower’s location is established by the orientation to north and the Summer Solstice, the Tower’s windows, by their location in the walls and their shapes, are no longer a mystery. From inside the Tower, on its first wooden floor, a person of about five feet five inches tall, standing in front of a point marked in the sill of the south window, could see the summit of Miantonomi Hill through the very small north window. Above the hill, in the sky in the same direction, is the North Star - Polaris.

So I guess it may not have ever been built, that "Long Isle" tower. Which would mean that the Newport one may be the only one built by the colonial people.