Charles Ellicott Commentary Ezra 4:20

"There have been mighty kings also over Jerusalem, who have ruled over all [the country] beyond the River; and tribute, custom, and toll, was paid unto them." — Ezra 4:20 (ASV)

Mighty kings. —David and Solomon, and some few kings down to Josiah, had extended their sway and made nations tributary (2 Samuel 8:0; 1 Kings 10:0; 1 Kings 10:0). The earlier kings’ names would perhaps be referred to historically, though not immediately connected with Persian annals.