a dextris tuis..

[Hermes Trismegistus]

(...) Cadent a latere tuo mille
et decem milia a dextris tuis;
ad te autem non appropinquabit.

Why is it in the plural and not only "a dextra tua" like "a latere tuo"?

 

[Mafalda]

It is a noun, n, pl.: dextra, dextrorum; it means that which is on the right. Like omnia, for example. Omnia mea = all that I have. Dextra mea = that which is on my right.