πολλὰ παρὰ πολλοῖς ἔθη καὶ νόμους ἀναγράφων

I met a sentence:
“Ποσειδώνιος ὁ ἀπὸ τῆς Στοᾶς, ἐν ταῖς Ἱστορίαις πολλὰ παρὰ πολλοῖς ἔθη καὶ νόμους ἀναγράφων.”

I wonder that what does “πολλὰ” modify here, “ἔθη καὶ νόμους”? And “παρὰ πολλοῖς” what?

The next paragraph is:

“Κέλται, φησί, τὰς τροφὰς προτίθενται χόρτον ὑποβάλλοντες ἐπὶ τραπεζῶν ξυλίνων μικρὸν ἀπὸ τῆς γῆς ἐπηρομένων. Ἡτροφὴ δ’ ἐστὶν ἄρτος μὲν ὀλίγος, κρέα δὲ πολλά. Προσφέρονται δὲ ταῦτα ὥσπερ οἱ λέοντες ταῖς χερσὶν ἀμφοτέραις αἵροντες ὅλα κρέα καὶ ἀποδάκνοντες, τὰ δὲ δυσαπόσπαστα μαχαίρᾳ μικρᾷ παρατέμνοντες.”

Yes, πολλὰ goes with ἔθη καὶ νόμους. πολλοῖς just means ‘many people’, or ‘many peoples’ as we’d say in English (with the Celts following as an example).

Thanks.
Another question: why “ἀναγράφων” here?
I guess it is not a sentence and “ἀναγράφων” here is to modify “Ποσειδώνιος”. But why in plural?

It’s the nominative singular present participle of ἀναγράφω

lol
I made a silly mistake.