This is what Josephus relates regarding the Jewish temple in Egypt:
So Ptolemy complied with his proposals, and gave him a place one hundred and eighty furlongs distant from Memphis. That Nomos was called the Nomos of Hellopolls, where Onias built a fortress and a temple, not like to that at Jerusalem, but such as resembled a tower. He built it of large stones to the height of sixty cubits; he made the structure of the altar in imitation of that in our own country, and in like manner adorned with gifts, excepting the make of the candlestick, for he did not make a candlestick, but had a [single] lamp hammered out of a piece of gold, which illuminated the place with its rays, and which he hung by a chain of gold; but the entire temple was encompassed with a wall of burnt brick, though it had gates of stone. The king also gave him a large country for a revenue in money, that both the priests might have a plentiful provision made for them, and that God might have great abundance of what things were necessary for his worship. Yet did not Onias do this out of a sober disposition, but he had a mind to contend with the Jews at Jerusalem, and could not forget the indignation he had for being banished thence. Accordingly, he thought that by building this temple he should draw away a great number from them to himself. There had been also a certain ancient prediction made by [a prophet] whose name was Isaiah, about six hundred years before, that this temple should be built by a man that was a Jew in Egypt.
Josephus, Wars, Book VII, Ch. 10.3
Josephus hear mentions that:
1) Onias constructed his temple so it did not resemble the Temple in Jerusalem, and
2) that this was a deliberate attempt to get revenge for being exiled.
Could Onias, then, have converted to Samaritanism? Compare what Josephus says about the temple to this image of the temple of Gerizim below. Notice the exceptionally high tower soaring beyond its walls.
Also note the passage in
Isaiah, ch. 19:
In that day there will be an altar to the Lord in the midst of the land of Egypt, and a pillar to the Lord at its border. It will be a sign and a witness to the Lord of hosts in the land of Egypt. When they cry to the Lord because of oppressors, he will send them a savior and defender, and deliver them. And the Lord will make himself known to the Egyptians, and the Egyptians will know the Lord in that day and worship with sacrifice and offering, and they will make vows to the Lord and perform them. And the Lord will strike Egypt, striking and healing, and they will return to the Lord, and he will listen to their pleas for mercy and heal them.
Despite evidence that Jews had already a temple in Egypt dating to the fifth century, bc (the
Elephantine papyri), rabbinical literature states that Onias and his temple, was solely and directly influenced by this passage in Isaiah.
This then opens a question for me...
Was portions of
Isaiah Samaritan focused, written in the second century, bc?