It looks strange for me to name any settlement after a mud.
Never exclude `vulgarism` when enter in the head of ancients. They were blunt, primordial, sincere, clear. For example, Serbs would say KURAJBER for the 9 the generation back in family (son, father, grandfather.... 9th generation). Word is in use even today and had to be old as time itself is old. KURAJBER is from KURAC (literally - di*k), One Who Have D*ck. So, ancients who invented word considered their 9th ancestor the One Who Have D*ck. See now why is Serbian oldest Slavic and European language.
But, in this case I would bet on BRLOG and also very possible BRVNO as original.
BRVNO is wooden trunk, with removed branches, ready for use in building the wooden house- log cabin. So, if you build wooden settlement you would maybe eant to name it BRVNO, or how I see that R is softened among Northern Serbs, it went to BERVNO.
But, I would still bet on BRLOG. Its in connection to animistic belief of ancients in animal protector. They built settlement and it was their house. They just sanctified it by giving name BRLOG, house of the Bear. That gave them sense of power and security. It had to be BRLOG.
In modern day Serbian... Let me give you some more ancient Sarmatian ..
1 - SIN (son), 2 - OTAC (father), 3 - DEDA (grandfather), 4 - PRADEDA, 5 - ČUKUNDEDA, 6 - ASKURDJEL, 7 - SUKURDJEL, 8 - REBALO, 9 - KUREBALO, 10 - KURAJBER, 11 - BELI ORAO (white eagle). It is ancient and it is today. Spot how KUR (di*k) is usual and at the 11th generation you have trace of animism, most admired animal protector- eagle.
Sorry, my mistake. KURAJBER is 10th generation before son. Most words I even can`t translate in English because don`t even exist in English. That way of thinking is with time lost in English, that is very young comparing to Slavic languages and Serbian.