What is a "free baron"?

Question:

What is a "free baron"?

In a book written by my [4th] great grandfather he calls himself a free baron of dover?

Anyone know what this means?

Additional Details

2 months ago
His name was Kennett Beecham Martin,he was a Captain.

Could it have something to do with his maritime battles?

2 months ago
He also mentions in the book:

'my grandfather,also,fond of reciting to us all he knew of ancient traditions from his father,who was a doctor and scholar;and as my venerable ancestor was born in the reign of queen anne,and remembered Dover
before the innovations of the first american war ,which levelled some of its old ruins to erect batteries,we were arrested by his descriptions'

1 month ago
no merc that is an older post of mine.

Best Answer - Chosen by Asker: 2 months ago
His name was Kennett Beecham Martin,he was a Captain.

Could it have something to do with his maritime battles?