Though the four-day-long DefExpo, on the outskirts of Chennai and close to the temple town of Mahabalipuram on the East Coast Road, began yesterday amid protests on the Cauvery issue, it was formally inaugurated by Prime Minister Narendra Modi today. Defence Minister Nirmala Sitharaman had launched the exhibition yesterday. When PM Modi reached Chennai this morning to head to the DefExpo near Mahabalipuram, DMK working president MK Stalin asked supporters and residents to show black flags atop their homes in a sign of protest against the Centre's "inaction" on the Cauvery issue.