Vegetation growth on archaeological monuments constitutes a major conservation and preservation problem. In certain cases it can perform a highly destructive role in its physical integrity (CATIZONE and TIBILETTI, 1998). In Tróia archaeological site (Portugal), a conservation programme is being implemented due to a lack of maintenance during ten years. This situation caused occultation of the monuments and their severe disintegration. Results of the field studies carried out for five years are presented. Mechanical weed control together with chemicals methods (glyphosate, glyphosate+triclopyr, glyphosate+isoxaben, metsulfuron-methyl and triclopyr) applied with different methodologies and periods of application, showed good results on the control of the main weeds developed among several monuments.