Is Plato's account of Atlantis true or not?

It is often claimed that Plato used his story about Atlantis merely as a fantasy about a non existing land to express his views about political systems. But then he says himself: “This tale about Atlantis, though strange, is certainly true, having been attested by Solon, who was the wisest of the seven sages.”
Why would he explicitly say so if this account would not be true.
Especially, if we consider that honour and truth in his day were held higher than the value of life. Solon, an ancestor of Plato and reputedly the inventor of Democracy, had been to Egypt and there

the priests had told him about Atlantis. Via Solon this account about Atlantis came to Plato. We need to be realistic: Even in Plato’s day anyone could have traveled to Egypt to verify what was said about Atlantis. Plato was a reputable philosopher and statesman – he had no reason to jeopardize his status by inventing a myth.

Furthermore, if one insisted that the great Plato told mere fantasies to play off his political ideas, then why would he have gone to such detail like: inventing a tale of 5 pairs of twins giving them fantasy names, how wide was each land - or water ring, how wide was the canal, how wide was a bridge, with what colour stone were the buildings constructed, what type of brass was used where, where did the water come from and how was it distributed…. All this is utterly unnecessary if one wants to explain a political system.

Plato is accepted as one of mankind’s greatest philosophers, therefore one should assume that he wrote the truth.