Greg Smith's first LV= County Championship century for Essex guided the visitors into a strong position on the opening day against Gloucestershire at Bristol.
The 30-year-old hit an unbeaten 149 as his side ran up 333 for seven after losing the toss.
Owais Shah contributed 34 and Ben Foakes 32, while Will Gidman and David Payne claimed two wickets apiece for Gloucestershire.
Former Derbyshire batsman Smith was dropped on 19 by Michael Klinger at third slip off Payne and went on to face 274 balls, hitting 17 fours and a six.
With the skies overcast, Gloucestershire skipper Klinger elected to field first and saw his seamers bowl without much luck in the morning session.
Gidman went past the bat on a number of occasions, but did have the satisfaction of bowling India Test player Gautam Gambhir off an inside edge for a duck with the total on nine.
It was 46 for two in the 15th over when Jaik Mickleburgh, on 26, was well caught by wicketkeeper Gareth Roderick, having got an inside edge to a delivery from Graeme McCarter.
McCarter had received a late call into Gloucestershire's team when Liam Norwell withdrew because of a groin injury.
Smith survived his second chance on 41 when Gidman failed to hold a tough one-handed catch at gully off Craig Miles and went on to a half-century off 98 balls, with four fours, having spent 21 deliveries on 48.
Shah looked in confident form as the pair added 80 either side of lunch. Yet with the score on 126 he played down the wrong line to Miles and was pinned lbw, having hit seven fours in a fluent 72-ball knock.
Ryan ten Doeschate helped Smith put on a further 45 in nine overs, contributing 24 to the stand, before edging Benny Howell to Roderick on the drive.
Smith moved relentlessly towards his ton and reached it with a sweet cover-driven four off McCarter, having faced 207 balls and extended his boundary count to 10 fours and a six.
In his second season with Essex, Smith's previous best championship score for the county was 42 against Hampshire last season. He played with increasing sureness and began to cut loose after reaching three figures.
Gloucestershire took the new ball in the 81st over with Essex 259 for four and Gidman struck with it as Foakes edged to Chris Dent in the slips.
Foakes had ridden his luck at times, facing 84 balls and striking four fours in a stand of 94 with Smith. James Foster looked more assured, but edged Payne up in the air on 26 and Klinger took the catch running back from gully.
Graham Napier fell to what proved the last ball of the day, caught by Dent off Payne for 10.