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We present a quantitative analysis of the SFH of 12 fields in the SMC. Wefind that there are four main periods of enhancement of star formation: a youngone peaked at around 0.2-0.5 Gyr old, only present in the eastern and in thecentral-most fields; two at intermediate ages present in all fields (aconspicuous one peaked at 4-5 Gyr old, and a less significant one peaked at1.5-2.5); and an old one, peaked at 10 Gyr in all fields but the western ones.In the western fields, this old enhancement splits into two, one peaked ataround 8 Gyr old and another at around 12 Gyr old. This "two-enhancement" zoneseems to be a robust feature since it is unaffected by our choice of stellarevolutionary library but more data covering other fields of the SMC arenecessary in order to ascertain its significancy.  Some correlation could exist with encounters taken from the orbitdetermination of Kallivayalil et al. (2006). But our results would be also fitin a first pericenter passage scenario like the one claimed by Besla et al.(2007). There is a strong dichotomy between East/Southeast and West in thecurrent irregular shape of the SMC. We find that this dichotomy is produced bythe youngest population and began about 1 Gyr ago or later. We do not find yeta region dominated by an old halo at 4.5 kpc from the SMC center, indicatingeither that this old stellar halo does not exist in the SMC or that itscontribution to the stellar populations, at the galactocentric distances of ouroutermost field, is negligible. We derive the age-metallicity relation and findthat the metallicity increased continuously from early epochs until now.

Old Main Sequence Turnoff Photometry in the Small Magellanic Cloud. II. Star Formation History and Its Spatial Gradients