Tyre would be forgotten for a period of 70 years. It is uncertain if this means a literal number of years. It is possible that 70 merely indicates a long time, with 70 being used idiomatically to indicate the fullness of time.
The days of one king
sounds like the reigning period of a king, but 70 years is an extraordinarily long time for one king to reign. It may also indicate the average lifespan of man.
15 En ce temps-là, Tyr tombera dans l'oubli soixante-dix ans, Ce que dure la vie d'un roi. Au bout de soixante-dix ans, il en sera de Tyr Comme de la prostituée dont parle la chanson: