This quote is from the Historia Ierusalem Baldrici Dolensis Archiepiscopi, Book 2 (pg. 1092 of Migne, Patrologia Latina, CLXVI).
Your quote is only a fragment of the relevant sentence, which is likely why you are not able to make any sense of it. Here is the full sentence:
Iter enim aggressi, gradiebantur rependo per montana, nimis aspera et scopulosa, per quae nec eorum phalanges poterant, sicut heri et nudiustertius, seriatim procedere, nec eorum clitellariis dabatur saltem repere posse, sed miserrime hi et illi praegravabantur, neque siquidem illis in angusto positis, aliud erat aliunde diverticulum.
Here is my translation: I have purposely separated the long sentence into shorter ones that are better adapted to English syntax.
Having begun the journey, they advanced, crawling through the mountainous area, which was exceedingly perilous and craggy. Their battalions could not, like yesterday and the day before, proceed in a file, nor was it possible for their pack animals even to crawl forward through this area. Rather, they both were miserably encumbered, and there was not even an alternate route starting from elsewhere, since they were in a narrow area.
Two minor doubts on my part (comments welcome):
- phalanges can be a "battalion" or also a "pole for carrying burdens" or "rollers for transporting war machinery" (see L&S). It's very possible that the latter is intended.
- I'm not entirely certain why siquidem is used: I am translating it as if it were quidem.