[@sambauers Participant 18 years, 4 months ago]

Try:

RewriteRule ^/forums/viewtopic.php?t=([0-9]+)$

/forums/topic/$1 [R]

Escaping the dot and the dollar-sign. You might also need to specify:

RewriteBase /directory/path/where/forum/resides/

Just after “RewriteEngine on”