Significados de vitrify forts en inglés

Will Clerk says he has a theory on the vitrified forts.

These few examples will be enough to give some idea of the strange vitrified forts.

The vitrified forts surrounding England, but not in England.

The vitrified forts of Scotland, Ireland, Brittany, and Bohemia.

In the vitrified forts of a few parts of Europe, we find data that the Humes and Gibbons have disregarded.

But some of the vitrified forts are not upon tops of hills: some are very inconspicuous: their walls too are vitrified in streaks.

If so, we shall have to admit that vitrified forts date from the earliest centuries of the Christian era, and are not prehistoric at all.