In those days, as King Ahasuerus sat on his royal throne in Susa ¹  the citadel, ² 

biblegateway Est 1:2

in those days as King Ahasuerus sat on his royal throne which was at the citadel in Susa,

In those days King Ahasuerus reigned from his royal throne in the fortress at Susa.

At the time when King Xerxes sat on the royal throne in the fortress of Susa,

biblegateway Est 1:2

At that time King Xerxes reigned from his royal throne in the citadel of Susa,

in those days when King Ahasuerus sat on his royal throne in Susa, the capital,

bibleoremus Est 1:2

In those days when King Ahasuerus sat on his royal throne in the citadel of Susa,

at the time when he was settled on the royal throne in Susa, the capital city.

biblegateway Est 1:2

in those days when King Ahasuerus sat on the throne of his kingdom, which was in Shushan the citadel,

[That] in those days, when the king Ahasuerus sat on the throne of his kingdom, which [was] in Shushan the palace,

biblegateway Est 1:2

In those days, as King Ahasuerus sat on his royal throne in Susa ¹  the citadel, ² 

¹ tn Heb “Shushan” (so KJV, ASV). Most recent English versions render this as “Susa.”

¹ sn The city of Susa served as one of several capitals of Persia during this time; the other locations were Ecbatana, Babylon, and Persepolis. Partly due to the extreme heat of its summers, Susa was a place where Persian kings stayed mainly in the winter months. Strabo indicates that reptiles attempting to cross roads at midday died from the extreme heat (Geography 15.3.10-11).

² tn The Hebrew word בִּירָה (birah) can refer to a castle or palace or temple. Here it seems to have in mind that fortified part of the city that might be called an acropolis or citadel. Cf. KJV “palace”; NAB “stronghold”; NASB “capital”; NLT “fortress.”