בַּיָּמִ֖ים הָהֵ֑ם כְּשֶׁ֣בֶת ׀ הַמֶּ֣לֶךְ אֲחַשְׁוֵר֗וֹשׁ עַ֚ל כִּסֵּ֣א מַלְכוּת֔וֹ אֲשֶׁ֖ר בְּשׁוּשַׁ֥ן הַבִּירָֽה׃
that in those days, when the king Ahasuerus sat on the throne of his kingdom, which was in Shushan the castle,
Read kabbalistic (mystical) interpretation of Esther 1:2: and classical mystical sources.