sorry, dont know what went wrong. ill try again but less fancy. https://www.history.com/topics/halloween/history-of-halloween#:~:text=The%20tradition%20originated%20with%20the,of%20the%20traditions%20of%20Samhain.

and another incase that didnt work:
https://www.britannica.com/topic/Halloween

im no expert, i was just curious by what you said so looked it up. im doing so, i assumed that what you said about the romans having halloween in 600ish was true, and so when i read about Samhain and it coming before that, i reckoned the romans must have been influenced by the celts rather than the other way around, since Samhain does sound awfully halloweeny, what with the dressing up to ward off/fool spirits and the portals to the spirit world and such, (im scottish and was taught the last part as a child, i have no idea if that idea extends to america and elsewhere) whereas the roman festivals around the same time sound far less halloweeny.