Jeremiah 51:32

32. passages are stopped--The guarded fords of the Euphrates are occupied by the enemy (see on Jr 50:38). reeds ... burned--literally, "the marsh." After draining off the river, Cyrus "burned" the stockade of dense tree-like "reeds" on its banks, forming the outworks of the city's fortifications. The burning of these would give the appearance of the marsh or river itself being on "fire."

Robert Jamieson, A. R. Fausset & David Brown, 1871 · public domain

Verse 32 That the passages are stopped - Either the bridges or slips for boats, by which the inhabitants passed from one side to the other, and may mean the principal gates or passes in the city, which the victorious army would immediately seize, that they might prevent all communication between the inhabitants. The reeds they have burned with fire - What this means I cannot tell, unless it refer to something done after the taking of the city. Setting fire to the reeds in the marshy ground, in order the better to clear the places, and give a freer passage to the water, that it may neither stagnate nor turn the solid ground into a marsh. Dr. Blayney thinks it refers to the firing of the houses, in order to throw the inhabitants into the greater confusion; but no historian makes any mention of burning the city, except what is said Jer 51:30, "They have burned her dwelling places;" and this may be a poetical expression. That they burnt nothing before they took the city must be evident from the circumstance of their taking the city by surprise, in the night time, with the greatest secrecy. Still there might have been some gates, barricadoes, or wooden works, serving for barracks or such like, which obstructed some of the great passages, which, when they had entered, they were obliged to burn, in order to get themselves a ready passage through the city. This is the more likely because this burning of reeds is connected with the stopping of the passages, burning the dwelling places, and breaking the bars.

Adam Clarke, 1831 · public domain