I was looking deeper into the Seven Ancient Wonders of the World and came across Bede's account that added the Pharos of Alexandria to the lists that had been compiled by ancient writers. In his list, there are familiar wonders, like the Colossus of Rhodes and the Temple of Artemis at Ephesus. However, he also discusses a statue of Bellerophon on a horse that is suspended above a city purely through the use of magnetic stones, a bath heated by one continuously burning candle, and a theater carved from one piece of marble. I've never heard of any of these places before, and they seem pretty wondrous to me. He had to pull inspiration from somewhere, but I am having trouble finding any information on it. What are these wondrous places, and do they have real life equivalents or are they figments of medieval imaginations?
Bede (or should I say pseudo-Bede? I don't think the authorship question has been settled) wasn't quite the first to add the Pharos to the list: there are two others, of which the first is almost certainly earlier than Bede, and the second definitely is.
An anonymous poem in the Greek anthology, 9.656 (during or after the reign of Anastasius, early 6th century), which lists the seven wonders as:
Gregory of Tours, On the course of stars, preface (mid-to-late 6th century), giving the wonders as:
It's striking that both of these append the Pharos at the very end of the list; Bede puts it in second place. Bede's list has the 'Capitolium' in common with the Greek anthology poem; the theatre of Heraclea in common with Gregory of Tours; the temple of Artemis in common with the ancient lists; and the Colossus in common with all of them.
The long-and-short of it is that we don't have the full chain of influences and who copied their lists from where.
I've never seen any identification of Bede's Bellerophon statue or the heated baths. So I can't comment on their historicity -- other than to say that they seem to have come out of thin air. I've never seen any identification of the Rufinian grove in the Greek anthology poem either, and the 'Capitolian hall' (χάρις Καπετωλίδος αὐλῆς) is surely a fiction. But I hope it's of some use to you to have a bit more context for the addition of the Pharos to the seven.
Post script, a few minutes later:
I've just had a look in Kai Brodersen's 1999 book on Die sieben Weltwunder, and there are one or two other snippets that might be usefully added. First, you emphasis that Bede's theatre is carved from a single stone: this finds some parallel in a list in the 6th century Scholia Alexandrina (Brodersen p. 97), which includes as an eighth item a 'house made from a single stone with seven beds'. Possibly related.
He doesn't comment on Bede's Bellerophon statue, and about the self-heating baths he just makes a joke about Bede wanting self-heating baths in the climate of northern England ('man fragt sich unwillkürlich, ob ein solches Weltwunder im zugig-kalten Nordengland geradezu erfunden werden mußte!', p. 106).
Brodersen does do one useful thing, and that is to give a bunch more examples of lists of seven wonders from late antiquity and the mediaeval period. It's at least clear that everyone who made a list felt free to add and remove wonders.
Post post script: one additional innovation in Bede's list is that he quotes a much bigger size for the Colossus than any other figure we have for it. Strabo, Pliny, and Philon of Byzantium put its height at 70 cubits, or ca. 32.3 metres; pseudo-Hyginus makes it 90 feet, or 26.6 metres (he makes the pyramids shorter than this!); Bede's figure for the Colossus is 136 feet, which would be 40.2 metres if you reckon in Roman feet.