4 adjectives to describe lustrums

Let us sit with our hands on our mouths, a long, austere, Pythagorean lustrum.

These were the twenty-sixth pair of censors since the first institution of that office; and this the nineteenth lustrum.

The attempted alliance of political economy with art was a novel undertaking in that sixth lustrum of the past century, even by a man of Mr. Ruskin's eminence and fame in the world of letters.

The census, begun in the preceding year, was completed: this is said to have been the tenth lustrum that was completed from the date of the foundation of the city.

4 adjectives to describe  lustrums