user10380: As stated in this question, the convention that the player with the lighter-coloured pieces makes the first move was not established until fairly late in the 19th century.
Before then, what convention (if any) was there as to the placement of the kings and queens? For example, had the convention been established already, that if a player moved first, their king starts to the right of their queen?
Wikipedia is silent on this.

user17823: According to this translated version  of Libro de los Juegos ("Book of Games"), page 7:

And of the other pieces which are greater one resembles the king, who is the lord of the army and he should be in one of the two middle squares.
And next to him in the other middle square, is another piece which resembles the fers (alfferez) who carries the standard of the king's colours. And there are some men who do not know the name and call him "fersa" (alfferza). [...]

It's worth noting that the queen was originally called fers.

10380: <p>As <a href="https://chess.stackexchange.com/q/38737">stated in this question</a>, the convention that the player with the lighter-coloured pieces makes the first move was not established until fairly late in the 19th century.</p>
<p>Before then, what convention (if any) was there as to the placement of the kings and queens? For example, had the convention been established already, that if a player moved first, their king starts to the right of their queen?</p>
<p><a href="https://en.wikipedia.org/wiki/History_of_chess#Early_changes_to_the_rules" rel="nofollow noreferrer">Wikipedia</a> is silent on this.</p>
 17823: <p>According to <a href="http://jnsilva.ludicum.org/HJT2012/BookofGames.pdf" rel="noreferrer">this translated version</a>  of <a href="https://en.wikipedia.org/wiki/Libro_de_los_Juegos" rel="noreferrer"><em>Libro de los Juegos</em></a> (&quot;Book of Games&quot;), page 7:</p>
<blockquote>
<p>And of the other pieces which are greater one resembles the king, who is the lord of the army and he should be in one of the two middle squares.</p>
<p>And next to him in the other middle square, is another piece which resembles the fers (alfferez) who carries the standard of the king's colours. And there are some men who do not know the name and call him &quot;fersa&quot; (alfferza). [...]</p>
</blockquote>
<p>It's worth noting that the queen was originally called <a href="https://en.wikipedia.org/wiki/History_of_chess#Names_of_pieces" rel="noreferrer"><em>fers</em></a>.</p>
