Roman period thumb|250px|The theatre, restored by Pliny the Younger Along with the rest of Bithynia, Nicaea came under the rule of the Roman Republic in 72 BC. The city remained one of the most important urban centres of Asia Minor throughout the Roman period, and continued its old competition with Nicomedia over pre-eminence and the location of the seat of the Roman governor of Bithynia et Pontus. The geographer Strabo (XII.565 ff.) described the city as built in the typical Hellenistic fashion with great regularity, in the form of a square, measuring 16 stadia in circumference, i.e. approx. or covering an area of some or ; it had four gates, and all its streets intersected one another at right angles in accordance with the Hippodamian plan, so that from a monument in the centre all the four gates could be seen. This monument stood in the gymnasium, which was destroyed by fire but was restored with increased magnificence by Pliny the Younger, when he was governor there in the early 2nd century AD. In his writings Pliny makes frequent mention of Nicaea and its public buildings.
romAn PeRiod THumb|250pX|The ThEaTre, rEsTorED by plInY the yOuNGer alonG WiTh The ReSt of bITHynIa, nicaEa camE UndeR thE RulE Of thE RoMan rEPUBlic in 72 bC. the ciTy rEmaiNed oNe of tHe mOSt IMportant urban cenTreS of asIa Minor thrOughoUT The ROman perioD, AnD conTiNuEd its oLd comPetiTioN wiTH niComediA oVER Pre-eMinEncE anD thE locaTIoN oF the seat of ThE RomaN goverNOR oF biThYNiA et pOnTUS. the geOgRAPHer sTrAbO (xIi.565 Ff.) dEscribEd the cIty as bUiLt iN The TyPiCAl HELleNIStIc fAshioN with greAt ReguLaRitY, IN the foRm OF A sQUare, Measuring 16 sTaDia in CircumfErence, i.e. APprox. or coverinG an area Of sOMe oR ; it haD FoUr GAtes, aND all ItS StReeTS InterSecTed oNE anotHer aT riGHt anglES in aCcordance with the hIPPoDaMian Plan, so THaT fRom a MonuMent iN the ceNtre alL tHE fOUr gAtes could be seEn. tHIs moNuMeNt stoOd in thE gyMnasIum, wHICH was destroYEd bY firE bUT was restorEd With incReased MagnifICeNce by pLiny tHe younGer, wHeN hE waS governOr there in ThE Early 2ND ceNtury ad. iN hIs writinGs plIny mAKeS FrEqueNt meNtiOn of NiCaea and Its pUblic buildinGs.