They were repaired with the advice from Soviet engineers and the new design, dubbed the iron dam, was considered unbreakable.

The fortress was besieged several times in its history and was considered unbreakable.

His cipher marked an epoch and was considered unbreakable for four centuries.

Young is the all-time leader in wins with 511, a mark that is considered unbreakable.

Like everybody, Jack understood that super-strong encryption was considered unbreakable.

While he still remains in the top 10 all-time for scoring at Hofstra, his rebounding mark is considered unbreakable.

This is the race she really wants in Sydney, the 100 butterfly, perhaps to break yet again a record that was once considered unbreakable.

Cryptographers have drawn on this fact to develop codes considered all but unbreakable.

That summer some seniors wondered if an Ingersoll watch, considered unbreakable, could withstand being dropped from the chapel.

The running key variant of the Vigenère cipher was also considered unbreakable at one time.