What do you mean by this phrase?

The phrase is 'a thicket of symbols'. And the sentence was 'To begin with, the first page of 'The Hobbit' was a thicket of symbols, to be decoded one at a time and joined hesitantly together.' Now waht is the exact meaning of this phrase in this sentence and what would be the synonym of thicket as it is used in this text. Thank you:)