I mean to play on map 1000x1000 or biggest with a lot of other civilizations.
Civ3 can't run maps quite
that big: IIRC, the biggest map you can make in the standard Firaxis editor is 362*362.
There are several map-mods which use larger-than-Firaxis-Huge maps: Off the top of my head,
@Marla_Singer's Earthmap (made for PTW, but usable in Conquests; it just lacks Volcanoes and Marsh) is around 180*180,
@Yoda Power's Earthmap is something like 256*256 (and has all 31 Civs historically placed); and
@LKendter also made an Earthmap-mod (based on Yoda's?) which renames the original Civs, and spreads them out more widely (e.g. the English are now the "Australians").
For full mods,
@AnthonyBoscia's WorldWide mod and
@Civinator's own total-conversion CCM mod, and his curated RARR mod, also allow play on Huge+ maps with >16 Civs.
Bear in mind though, that using the standard Conquests .exe, all maps are subject to the maximum 512 city-limit. After that limit is reached, no more cities can be founded. There are some hacked executables out there which theoretically allow that limit to be breached, but they don't all work 100% correctly.