Erasmus's letter 1756 (readable in its entirety here) describes an explosion of gunpowder in a castle at Basel. I'm having trouble understanding a five-word phrase in the letter. This is the passage:
Vidisses immania fragmenta turris, avium ritu, volitare per aera; quaedam ad ducentos passus deferri, qua dabatur liberum aeris spatium; alia civium domos longo tractu demoliri.
"You would have seen huge fragments of the tower, like birds, flying through the air; some of which were carried up to two hundred paces away, qua dabatur liberum aeris spatium; others destroyed the houses of citizens over a wide area."
What is meant by qua dabatur liberum aeris spatium?