In this paper we report on the data recorded with the first Antares detector line. The line was deployed on the 14th of February 2006 and was connected to the readout 2 weeks later. Environmental data for one and a half years of running are shown. Measurements of atmospheric muons from data taken from selected runs during the first 6 months of operation are presented. Performance figures in terms of time residuals and angular resolution are given. Finally the angular distribution of atmospheric muons is presented and from this the depth profile of the muon intensity is derived. ; 7 pages, 9 figures.-- ISI Article Identifier: 000266336300004.-- Printed version published May 2009.-- et al.(ANTARES Collaboration).-- ArXiv pre-print available at: http://arxiv.org/abs/0812.2095 ; The authors acknowledge the financial support of the funding agencies: Centre National de la Recherche Scientifique (CNRS), Commissariat à l’Energie Atomique (CEA), Commission Européenne (FEDER fund and Marie Curie Program), Région Alsace (contrat CPER), Région Provence-Alpes-Côte d’Azur, Département du Var and Ville de La Seyne-sur-Mer, in France; Bundesministerium für Bildung und Forschung (BMBF), in Germany; Istituto Nazionale di Fisica Nucleare (INFN), in Italy; Stichting voor Fundamenteel Onderzoek der Materie (FOM), Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO), in The Netherlands; Russian Foundation for Basic Research (RFBR), in Russia; National Authority for Scientific Research (ANCS) in Romania; Ministerio de Ciencia e Innovación (MICINN), in Spain. We also acknowledge the technical support of Ifremer, AIM and Foslev Marine for the sea operation and the CC-IN2P3 for the computing facilities.